Knowledge of input and output shaft speeds for an automatic transmission would enable its control unit to execute smooth transmission shifts leading to enhanced vehicle performance. Although output-shaft speed measurement of an automatic transmission is easily accomplished, speed measurement of its input shaft is difficult due to the transmission complexity and its input shaft inaccessibility. Current methods for input-shaft speed measurement, such as the ones described in U.S. Pat. Nos. 6,522,133B1, 4,586,401 and 3,845,671, require a magnetic sensor that senses either the rotation of a large magnetic target wheel through a non-ferromagnetic reaction shell or the rotation of a transmission output gear. These solutions require sensors that are bulky and expensive for sensing rotating target wheels at great distances, expensive magnetic target wheels due to their large size, the use of an expensive non-ferromagnetic reaction shell, and placement of sensors through a hole on the transmission housing that requires robust sealing methods. Also, in certain designs where the large air-gap between the sensor and the target wheel requires the choice of a VR speed sensor, the resulting output signal does not allow low speed measurements.
USPTO Backgrounds
USPTO Backgrounds