DENKISHANOINBAATASEIGYOSOCHI

摘要

PURPOSE:To detect fault of a speed sensor reliably even at a low speed, by providing a means for detecting the abnormality of a speed sensor based on whether a signal state representing the vehicular speed corresponding to a commanded slip frequency is established under powering operation. CONSTITUTION:Rotation frequencies f1-f4 of induction motors 2 are fed through a frequency selecting/switching section 9 to a minimum value selecting section 10 and a maximum value selecting section 11. When the highest frequency in the rotation frequencies f1-f4 is higher than 10Hz, a highest frequency judging section 6 produces a signal. A speed sensor exhibiting the minimum value when the difference between the highest and lowest frequencies exceeds over 10Hz is judged to be faulty through a frequency comparing section 7. A speed sensor exhibiting rotation frequency lower than a predetermined value upon elapse of predetermined time after provision of a powering command is judged to be faulty through a frequency detecting section 19.