Diagnostic method for diagnosing sticking of canister purge valve and automotive diagnostic system therefor

1. A diagnostic method of diagnosing sticking of a canister purge valve in an automotive diagnostic system in a vehicle comprising:

controlling, by an engine control unit, opening and closing of the canister purge valve in order to diagnose sticking of the canister purge valve,

calculating, by the engine control unit, a throttle learning value of the canister purge valve for acquiring a variation of an amount in an air inflow flowing into the engine in each of a first control section, a second control section, and a third control section;

comparing, by the engine control unit, throttle learning values calculated in each of the control sections;

acquiring, by the engine control unit, the variation of the amount in the air inflow flowing into the engine at the time of opening and closing of the canister purge valve; and

determining, by the engine control unit, whether the canister purge valve is stuck based on the variation of the amount in the air inflow, wherein the determining comprises:

acquiring an amount of a first air inflow flowing into the engine based on an output value of the intake pressure sensor in one of the control sections,

acquiring an amount of a second air inflow flowing into the engine based on an opening angle of the throttle in one of the control sections, and

calculating the throttle learning value of the canister purge valve by comparing the amount of the first air inflow with the amount of the second air inflow, and

determining whether the canister purge valve is stuck by comparing a variation in the throttle learning value with a threshold value,

wherein the automotive diagnostic system in the vehicle uses the determination to monitor the canister purge valve to diagnose a faulty condition to reduce exhaust emissions from the vehicle.

2. The diagnostic method according to claim 1 , wherein calculating the throttle learning value comprises:

calculating a first learning value of the canister purge valve in the first control section where the canister purge valve is set to open;

calculating a second throttle learning value of the canister purge valve in the second control section where the canister purge valve is set to be switched from opening to closing; and

calculating a third throttle learning value of the canister purge valve in the third control section where the canister purge valve is set to be switched from closing to opening.

3. The diagnostic method according to claim 2 , wherein the variation of the amount in the air inflow is acquired based on the first throttle learning value, the second throttle learning value and the third throttle learning value.

4. The diagnostic method according to claim 3 , wherein if the amount of the air inflow is varied such an extent that a difference between the third throttle learning value and the first throttle learning value is smaller than a predetermined first threshold value and a difference between the second throttle learning value and the first throttle learning value is greater than a predetermined second threshold value, it is determined that the canister purge valve is stuck.

5. The diagnostic method according to claim 1 , wherein if the steady state condition is maintained in each of the control sections, the step of calculating the throttle learning value proceeds to a next control section.

6. The diagnostic method according to claim 5 , wherein a control factor value for determining whether the steady state condition is satisfied is saved at the end point of each of the control sections.

7. The diagnostic method according to claim 6 , wherein the control factor value includes the throttle learning value and at least one of the number of engine rotation, an intake air amount of an engine, a target intake air amount of an engine, a throttle opening amount and a throttle opening target value.

8. The diagnostic method according to claim 7 , wherein the control factor values except for the throttle learning value, which are acquired in each of the control sections, are compared with each other between adjacent control sections and if a difference therebetween is equal to or smaller than a threshold value, the throttle learning values are compared with each other.

9. The diagnostic method according to claim 1 , further comprising:

determining whether a diagnosis activation condition of the canister purge valve is satisfied during running of a vehicle, wherein the diagnosis activation condition includes

a condition that a primary diagnosis for diagnosing sticking of the canister purge valve, based on a proportion that a fuel quantity compensating value accounts for in a total fuel injection amount under the state that the canister purge valve is opened above a flow rate, fails;

a condition that a period of time elapses after the preceding diagnosis is carried out;

a condition that both the amount of air inflow and the throttle learning value become stable;

a condition that flow rate of the canister purge valve is a predetermined rate or more;

a condition that a level of canister loading is a predetermined level or less; and

a condition that catalyst temperature is equal to or higher than a predetermined temperature.

10. A diagnostic method for diagnosing sticking of a canister purge valve in an automotive diagnostic system in a vehicle comprising:

carrying out a primary diagnosis for diagnosing sticking of the canister purge valve, based on a proportion that a fuel quantity compensating value accounts for in a total fuel injection amount under a state that the canister purge valve is opened above a flow rate; and

carrying out a secondary diagnosis for diagnosing sticking of the canister purge valve, wherein opening and closing of the canister purge valve are controlled in one of a plurality of control steps and throttle learning values calculated for acquiring a variation of an amount in an air inflow of an engine are monitored based on an intake air pressure sensor and a throttle opening amount in each of the control sections,

wherein the primary diagnosis and the secondary diagnosis are carried out when a common condition is satisfied, the common condition including:

a condition that diagnosis of the canister purge valve is not completed,

a condition that the intake air pressure sensor and an atmospheric pressure sensor are in a steady state, a condition that the number of engine rotation is constant,

a condition that altitude is equal to or less than a predetermined level,

a condition that voltage of a vehicle battery is normal, and

a condition that temperatures of the outside air and engine cooling water are normal,

wherein the automotive diagnostic system in the vehicle uses the primary diagnosis and the secondary diagnosis to monitor the canister purge valve to diagnose a faulty condition to reduce exhaust emissions from the vehicle.

11. The diagnostic method according to claim 10 , wherein the primary diagnosis is carried out when conditions that a level of canister loading is constant and flow rate of the canister purge valve is equal to or greater than a predetermined flow rate are satisfied.

12. The diagnostic method according to claim 10 , wherein the secondary diagnosis is carried out when an air amount test condition is satisfied, the air amount test condition including

a condition that the result of the primary diagnosis fails;

a condition that a period of time elapses after the preceding diagnosis is carried out;

a condition that both the amount of air inflow and the throttle learning value become stable;

condition that flow rate of the canister purge valve is a predetermined flow rate or more;

a condition that a level of canister loading is a predetermined level or less; and

a condition that catalyst temperature is equal to or higher than a predetermined temperature.

13. The diagnostic method according to claim 10 , wherein carrying out the secondary diagnosis comprises:

controlling opening and closing of the canister purge valve and calculating throttle learning values in each of control sections in order to diagnose sticking of the canister purge valve;

comparing the throttle learning values calculated in each of control sections with each other;

acquiring a variation of an amount in an air inflow flowing from the canister purge valve when the canister purge valve is opened and closed; and

determining whether the canister purge valve is stuck based on the variation of the amount in the air inflow.

14. An automotive diagnostic system in a vehicle for diagnosing sticking of a canister purge valve comprising:

a canister for collecting evaporative gas generated in a fuel tank;

a canister purge valve for supplying the evaporative gas in the canister to an engine intake port;

an intake air pressure sensor for measuring an intake air amount flowing into an engine; and

an engine control unit for performing control for diagnosing sticking of the canister purge valve,

wherein the engine control unit controls opening and closing of the canister purge valve and calculates throttle learning values for acquiring a variation of an amount in an air inflow flowing into the engine in each of control sections;

compares the throttle learning values calculated in each of the control sections with each other;

acquires the variation of the amount in an air inflow flowing from the canister purge valve when the canister purge valve is opened and closed; and

determines whether the canister purge valve is stuck based on the variation of the amount in the air inflow,

wherein the engine control unit acquires an amount of a first air inflow flowing into the engine based on an output value of the intake air pressure sensor in one of the control sections;

acquires an amount of a second air inflow flowing into the engine based on an opening angle of the throttle in one of the control sections; and

calculates a throttle learning value of the canister purge valve by comparing the amount of the first air inflow with the amount of the second air inflow,

wherein the automotive diagnostic system in the vehicle uses the determination to monitor the canister purge valve to diagnose a faulty condition to reduce exhaust emissions from the vehicle.