Automatic transmission controller and automatic transmission control method

1. An automatic transmission controller for an automatic transmission, comprising:

a sensor input state evaluator configured to determine whether a sensor input signal is normal or abnormal, wherein the sensor input signal carries information about a measured vehicle state variable;

a vehicle speed calculator configured to:

calculate a predicted vehicle speed with reference to the measured vehicle state variable, in response to determination that the sensor input signal is normal;

calculate the predicted vehicle speed with reference to a first alternative value instead of the measured vehicle state variable, in response to determination that the sensor input signal is abnormal; and

calculate the predicted vehicle speed with reference to the measured vehicle state variable, in response to determination that the sensor input signal becomes normal after abnormal;

a target transmission ratio calculator configured to:

calculate a target transmission ratio with reference to the predicted vehicle speed, in response to determination that the sensor input signal is normal;

calculate the target transmission ratio with reference to a second alternative value instead of the predicted vehicle speed, in response to determination that the sensor input signal is abnormal;

calculate the target transmission ratio with reference to the second alternative value instead of the predicted vehicle speed, in response to determination that a predetermined condition is unsatisfied after the sensor input signal becomes normal after abnormal; and

calculate the target transmission ratio with reference to the predicted vehicle speed, in response to determination that the predetermined condition is satisfied after the sensor input signal becomes normal after abnormal; and

a transmission ratio controller configured to control the automatic transmission with reference to the target transmission ratio.

2. The automatic transmission controller as claimed in claim 1 , wherein the measured vehicle state variable is a measured vehicle speed.

3. The automatic transmission controller as claimed in claim 2 , wherein:

the automatic transmission shifts a ratio in rotational speed between an input shaft and an output shaft;

the input shaft is connected to a vehicle driving source;

the output shaft is connected to a vehicle driving wheel set;

the automatic transmission controller further comprises a vehicle speed sensor configured to measure an actual vehicle speed as the measured vehicle speed; and

the vehicle speed calculator includes:

a vehicle speed error calculator configured to calculate a vehicle speed error between the measured vehicle speed and an estimated vehicle speed;

a predicted vehicle speed calculator configured to calculate the predicted vehicle speed with reference to an integral of the vehicle speed error multiplied by a predetermined gain, wherein the predicted vehicle speed is a predicted value of a future vehicle speed a predetermined time period after a current time instant; and

an estimated vehicle speed calculator configured to calculate the estimated vehicle speed with reference to the predicted vehicle speed by applying a delay factor to the predicted vehicle speed, wherein the delay factor simulates a predetermined delay response.

4. The automatic transmission controller as claimed in claim 3 , wherein:

the automatic transmission controller further comprises a second sensor configured to measure a second measured vehicle state variable;

the sensor input state evaluator is configured to determine whether the sensor input signal as a first sensor input signal is normal or abnormal, and determine whether a second sensor input signal is normal or abnormal, wherein the second sensor input signal carries information about the second measured vehicle state variable;

the vehicle speed calculator is configured to:

calculate the predicted vehicle speed with reference to the measured vehicle speed and the second measured vehicle state variable, in response to determination that the first sensor input signal and the second sensor input signal are normal;

calculate the predicted vehicle speed with reference to a third alternative value instead of the second measured vehicle state variable, in response to determination that the second sensor input signal is abnormal; and

calculate the predicted vehicle speed with reference to the second measured vehicle state variable, in response to determination that the second sensor input signal becomes normal after abnormal; and

the target transmission ratio calculator is configured to calculate the target transmission ratio with reference to the predicted vehicle speed and the second measured vehicle state variable, in response to determination that the first sensor input signal and the second sensor input signal are normal.

5. The automatic transmission controller as claimed in claim 2 , wherein the first alternative value is a value of the measured vehicle state variable which is last obtained while it is determined that the sensor input signal is normal.

6. The automatic transmission controller as claimed in claim 2 , wherein:

the target transmission ratio calculator is further configured to:

calculate the target transmission ratio with reference to the measured vehicle speed, in response to determination that a measured vehicle driving state is within a predetermined region;

calculate the target transmission ratio with reference to the predicted vehicle speed, in response to determination that the measured vehicle driving state is out of the predetermined region;

calculate the target transmission ratio without reference to the predicted vehicle speed, in response to determination that the sensor input signal continues to be abnormal for a second predetermined time period after the sensor input signal becomes abnormal after normal; and

calculate the target transmission ratio with reference to the predicted vehicle speed, in response to determination that the sensor input signal becomes normal after abnormal, and the measured vehicle driving state is within the predetermined region.

7. The automatic transmission controller as claimed in claim 6 , wherein:

the automatic transmission controller further comprises an accelerator pedal opening sensor configured to measure an accelerator pedal opening; and

the predetermined region is a region in which the accelerator pedal opening is below a predetermined possible intermediate value.

8. The automatic transmission controller as claimed in claim 6 , wherein the predetermined region is a region in which the measured vehicle speed is below a predetermined possible intermediate value.

9. The automatic transmission controller as claimed in claim 1 , wherein:

the sensor input state evaluator is configured to determine whether the sensor input signal as a first sensor input signal is normal or abnormal, and determine whether a second sensor input signal is normal or abnormal, wherein the first sensor input signal carries information about the measured vehicle state variable as a first measured vehicle state variable, and the second sensor input signal carries information about a second measured vehicle state variable;

the vehicle speed calculator is configured to:

calculate the predicted vehicle speed with reference to the first measured vehicle state variable and the second measured vehicle state variable, in response to determination that the first sensor input signal and the second sensor input signal are normal;

calculate the predicted vehicle speed with reference to a third alternative value instead of the second measured vehicle state variable, in response to determination that the second sensor input signal is abnormal; and

calculate the predicted vehicle speed with reference to the second measured vehicle state variable, in response to determination that the second sensor input signal becomes normal after abnormal; and

the target transmission ratio calculator is configured to:

calculate the target transmission ratio with reference to the predicted vehicle speed, in response to determination that the first sensor input signal and the second sensor input signal are normal;

calculate the target transmission ratio with reference to the second alternative value instead of the predicted vehicle speed, in response to determination that the second sensor input signal is abnormal;

calculate the target transmission ratio with reference to the second alternative value instead of the predicted vehicle speed, in response to determination that a second predetermined condition is unsatisfied after the second sensor input signal becomes normal after abnormal; and

calculate the target transmission ratio with reference to the predicted vehicle speed, in response to determination that the second predetermined condition is satisfied after the second sensor input signal becomes normal after abnormal.

10. The automatic transmission controller as claimed in claim 1 , wherein the vehicle speed calculator is further configured to set the first alternative value with reference to a measured vehicle driving state when it is determined that the sensor input signal becomes abnormal.

11. The automatic transmission controller as claimed in claim 1 , wherein the first alternative value is a value of the measured vehicle state variable which is last obtained while it is determined that the sensor input signal is normal.

12. The automatic transmission controller as claimed in claim 1 , wherein the target transmission ratio calculator is further configured to set the second alternative value with reference to a measured vehicle driving state when it is determined that the sensor input signal becomes abnormal.

13. The automatic transmission controller as claimed in claim 1 , wherein the predetermined condition is a condition that a first predetermined time period is elapsed after determination that the sensor input signal becomes normal after abnormal.

14. An automatic transmission controller for an automatic transmission, comprising:

sensor input state evaluation means for determining whether a sensor input signal is normal or abnormal, wherein the sensor input signal carries information about a measured vehicle state variable;

vehicle speed calculation means for:

calculating a predicted vehicle speed with reference to the measured vehicle state variable, in response to determination that the sensor input signal is normal;

calculating the predicted vehicle speed with reference to a first alternative value instead of the measured vehicle state variable, in response to determination that the sensor input signal is abnormal; and

calculating the predicted vehicle speed with reference to the measured vehicle state variable, in response to determination that the sensor input signal becomes normal after abnormal;

target transmission ratio calculation means for:

calculating a target transmission ratio with reference to the predicted vehicle speed, in response to determination that the sensor input signal is normal;

calculating the target transmission ratio with reference to a second alternative value instead of the predicted vehicle speed, in response to determination that the sensor input signal is abnormal;

calculating the target transmission ratio with reference to the second alternative value instead of the predicted vehicle speed, in response to determination that a predetermined condition is unsatisfied after the sensor input signal becomes normal after abnormal; and

calculating the target transmission ratio with reference to the predicted vehicle speed, in response to determination that the predetermined condition is satisfied after the sensor input signal becomes normal after abnormal; and

transmission ratio control means for controlling the automatic transmission with reference to the target transmission ratio.

15. An automatic transmission control method for an automatic transmission, comprising:

determining whether a sensor input signal is normal or abnormal, wherein the sensor input signal carries information about a measured vehicle state variable;

calculating a predicted vehicle speed with reference to the measured vehicle state variable, in response to determination that the sensor input signal is normal;

calculating the predicted vehicle speed with reference to a first alternative value instead of the measured vehicle state variable, in response to determination that the sensor input signal is abnormal;

calculating the predicted vehicle speed with reference to the measured vehicle state variable, in response to determination that the sensor input signal becomes normal after abnormal;

calculating a target transmission ratio with reference to the predicted vehicle speed, in response to determination that the sensor input signal is normal;

calculating the target transmission ratio with reference to a second alternative value instead of the predicted vehicle speed, in response to determination that the sensor input signal is abnormal;

calculating the target transmission ratio with reference to the second alternative value instead of the predicted vehicle speed, in response to determination that a predetermined condition is unsatisfied after the sensor input signal becomes normal after abnormal;

calculating the target transmission ratio with reference to the predicted vehicle speed, in response to determination that the predetermined condition is satisfied after the sensor input signal becomes normal after abnormal; and

controlling the automatic transmission with reference to the target transmission ratio.