Gas detection apparatus and automatic ventilation system for vehicle

A gas detection apparatus using a gas sensor element whose electrical characteristics change in accordance with concentration of a specific gas, comprising:

• acquisition means for acquiring a sensor output value at predetermined cycle intervals by use of the gas sensor element, the sensor output value increasing with concentration of the specific gas;
• first calculation means for calculating a present first calculated value at the predetermined cycle intervals during a period in which a low-concentration signal is being generated, the present first calculated value representing a first calculated value at the present time, wherein
• when a present sensor output value representing a sensor output value at the present time is greater than an mth past first calculated value representing the first calculated value calculated in a past cycle preceding the present cycle by m cycles, the first calculation means calculates the present first calculated value by use of a first calculation expression on the basis of the present sensor output value,
• the first calculation expression includes:
• a reference term including at least one of a tracking term which, while tracking the sensor output value, changes more slowly than does the sensor output value, and an increasing term which gradually increases irrespective of changes in the sensor output value, and
• an increase-emphasizing term using the present sensor output value and determined in such a manner that the present first calculated value, calculated for a time series of sensor output values having an increase period in which the sensor output values increase monotonously and a decrease period subsequent to the increase period and in which the sensor output values decrease monotonously, becomes smaller, in the increase period, than a virtual present first calculated value for the time series by use of a virtual first calculation expression obtained through omission of the increase-emphasizing term, the present first calculated value decreasing with the rate of increase in the sensor output values of the time series, and, during the decrease period, the present first calculated value changing at a rate greater than a rate of change of the virtual present first calculated value, and
• when the present sensor output value is smaller than the mth past first calculated value, the first calculation means employs the present sensor output value as the present first calculated value;
• and
• high-concentration-signal generation means for generating a high-concentration signal in place of the low-concentration signal when the present sensor output value and the present first calculated value satisfy a predetermined first relation during the period in which the low-concentration signal is being generated.

A gas detection apparatus using a gas sensor element whose electrical characteristics change in accordance with concentration of a specific gas, comprising:

• acquisition means for acquiring a sensor output value at predetermined cycle intervals by use of the gas sensor element, the sensor output value decreasing as concentration of the specific gas increases;
• first calculation means for calculating a present first calculated value at the predetermined cycle intervals during a period in which a low-concentration signal is being generated, the present first calculated value representing a first calculated value at the present time and being calculated by use of a first calculation expression on the basis of a present sensor output value representing a sensor output value at the present time;
• the first calculation expression including:
• a reference term including at least one of a tracking term which, while tracking the sensor output value, changes more slowly than does the sensor output value, and a decreasing term which gradually decreases irrespective of changes in the sensor output value, and
• a decrease-emphasizing term using the present sensor output value and determined in such a manner that the present first calculated value calculated for a time series of sensor output values that are decreasing monotonously becomes greater than a virtual present first calculated value for the time series by use of a virtual first calculation expression obtained through omission of the decrease-emphasizing term, and the present first calculated value increases with the rate of decrease in the sensor output values of the time series;
• and
• high-concentration-signal generation means for generating a high-concentration signal in place of the low-concentration signal when the present sensor output value and the present first calculated value satisfy a predetermined first relation during the period in which the low-concentration signal is being generated.

A gas detection apparatus using a gas sensor element whose electrical characteristics change in accordance with concentration of a specific gas, comprising:

• acquisition means for acquiring a sensor output value at predetermined cycle intervals by use of the gas sensor element, the sensor output value decreasing as concentration of the specific gas increases;
• first calculation means for calculating a present first calculated value at the predetermined cycle intervals during a period in which a low-concentration signal is being generated, the present first calculated value representing a first calculated value at the present time, wherein
• when a present sensor output value representing a sensor output value at the present time is smaller than an mth past first calculated value representing the first calculated value calculated in a past cycle preceding the present cycle by m cycles, the first calculation means calculates the present first calculated value by use of a first calculation expression on the basis of the present sensor output value,
• the first calculation expression includes
• a reference term including at least one of a tracking term which, while tracking the sensor output value, changes more slowly than does the sensor output value, and a decreasing term which gradually decreases irrespective of changes in the sensor output value, and
• a decrease-emphasizing term using the present sensor output value and determined in such a manner that the present first calculated value, calculated for a time series of sensor output values having a decrease period in which the sensor output values decrease monotonously and an increase period subsequent to the decrease period and in which the sensor output values increase monotonously, becomes greater, in the decrease period, than a virtual present first calculated value for the time series by use of a virtual first calculation expression obtained through omission of the decrease-emphasizing term, the present first calculated value increasing with the rate of decrease in the sensor output values of the time series, and, during the increase period, the present first calculated value changing at a rate smaller than a rate of change of the virtual present first calculated value, and
• when the present sensor output value is greater than the mth past first calculated value, the first calculation means employs the present sensor output value as the present first calculated value;
• and
• high-concentration-signal generation means for generating a high-concentration signal in place of the low-concentration signal when the present sensor output value and the present first calculated value satisfy a predetermined first relation during the period in which the low-concentration signal is being generated.

A gas detection apparatus using a gas sensor element whose electrical characteristics change in accordance with concentration of a specific gas, comprising:

• acquisition means for acquiring a sensor output value S(n) at predetermined cycle intervals by use of the gas sensor element, the sensor output value S(n) increasing with concentration of the specific gas, where n is an integer representing the chronological order of each sensor output value in a time series of sensor output values;
• first base-value calculation means for calculating a base value B(n) at the predetermined cycle intervals during a period in which a low-concentration signal is being generated, the base value B(n) being calculated in accordance with Expression (1):
• B(n)=B(n−1)+k1[S(n)−B(n−1)]−k2[S(n)−S(n-q)] (1)
• where k1 and k2 are first and second coefficients, 0<k1<1, K2>0, and q is a positive integer;
• differential-value calculation means for calculating a difference value D(n) in accordance with Expression (2):
• D(n)=S(n)−B(n) (2)
• on the basis of the sensor output value S(n) and the base value B(n);
• and
• high-concentration-signal generation means for generating a high-concentration signal when the difference value D(n) is greater than a high-concentration threshold Tu.

A gas detection apparatus using a gas sensor element whose electrical characteristics change in accordance with concentration of a specific gas, comprising:

• acquisition means for acquiring a sensor output value S(n) at predetermined cycle intervals by use of the gas sensor element, the sensor output value S(n) increasing with concentration of the specific gas, where n is an integer representing the chronological order of each sensor output value in a time series of sensor output values;
• first base-value calculation means for calculating a base value B(n) at the predetermined cycle intervals during a period in which a low-concentration signal is being generated, wherein
• when the sensor output value S(n) is greater than a preceding base value B(n−1) representing a base value calculated in a preceding cycle, the first base-value calculation means calculates the base value B(n) in accordance with Expression (1):
• B(n)=B(n−1)+k1[S(n)−B(n−1)]−k2[S(n)−S(n-q)] (1)
• where k1 and k2 are first and second coefficients, 0<k1<1, K2>0, and q is a positive integer, and
• when the sensor output value S(n) is smaller than the preceding base value B(n−1), the first base-value calculation means calculates the base value B(n) in accordance with Expression (3):
• B(n)=S(n) (3);
• differential-value calculation means for calculating a difference value D(n) in accordance with Expression (2):
• D(n)=S(n)−B(n) (2)
• on the basis of the sensor output value S(n) and the base value B(n);
• and
• high-concentration-signal generation means for generating a high-concentration signal when the difference value D(n) is greater than a high-concentration threshold Tu.

A gas detection apparatus using a gas sensor element whose electrical characteristics change in accordance with concentration of a specific gas, comprising:

• acquisition means for acquiring a sensor output value S(n) at predetermined cycle intervals by use of the gas sensor element, the sensor output value S(n) decreasing as concentration of the specific gas increases, where n is an integer representing the chronological order of each sensor output value in a time series of sensor output values;
• third base-value calculation means for calculating a base value B(n) at the predetermined cycle intervals during a period in which a low-concentration signal is being generated, the base value B(n) being calculated in accordance with Expression (5):
• B(n)=B(n−1)+k5[S(n)−B(n−1)]−k6[S(n)−S(n-t)] (5)
• where k5 and k6 are fifth and sixth coefficients, 0<k5<1, K6>0, and t is a positive integer;
• differential-value calculation means for calculating a difference value D(n) in accordance with Expression (6):
• D(n)=B(n)−S(n) (6)
• on the basis of the sensor output value S(n) and the base value B(n);
• and
• high-concentration-signal generation means for generating a high-concentration signal when the difference value D(n) is greater than a high-concentration threshold Tu.

A gas detection apparatus using a gas sensor element whose electrical characteristics change in accordance with concentration of a specific gas, comprising:

• acquisition means for acquiring a sensor output value S(n) at predetermined cycle intervals by use of the gas sensor element, the sensor output value S(n) decreasing as concentration of the specific gas increases, where n is an integer representing the chronological order of each sensor output value in a time series of sensor output values;
• third base-value calculation means for calculating a base value B(n) at the predetermined cycle intervals during a period in which a low-concentration signal is being generated, wherein
• when the sensor output value S(n) is smaller than a preceding base value B(n−1) representing a base value calculated in a preceding cycle, the third base-value calculation means calculates the base value B(n) in accordance with Expression (5):
• B(n)=B(n−1)+k5[S(n)−B(n−1)]−k6[S(n)−S(n-t)] (5)
• where k5 and k6 are fifth and sixth coefficients, 0<k5<1, K6>0, and t is a positive integer, and
• when the sensor output value S(n) is greater than the preceding base value B(n−1), the third base-value calculation means calculates the base value B(n) in accordance with Expression (7):
• B(n)=S(n) (7);
• differential-value calculation means for calculating a difference value D(n) in accordance with Expression (6):
• D(n)=B(n)−S(n) (6)
• on the basis of the sensor output value S(n) and the base value B(n);
• and
• high-concentration-signal generation means for generating a high-concentration signal when the difference value D(n) is greater than a high-concentration threshold Tu.