| 摘要 |
PROBLEM TO BE SOLVED: To avoid unstable fluid pressure by driving a duty solenoid by a frequency other than a resonance frequency of a duty solenoid made of integral multiples or a factor of integral multiples of speed of an internal combustion engine. SOLUTION: During operating an engine, in a micro computer 1, a control duty ratio of a line pressure solenoid 23 according to an engine load and a vehicle traveling condition is calculated from output signals of an engine speed sensor 11, a throttle opening sensor 9, a car speed sensor 13, and the like. It is judged whether engine speed is a second engine speed prescribed value (about 5,800 rpm) or more or not. In the case of 'YES', it is judged whether the engine speed is a third engine speed prescribed value (about 6,100 rpm) and less or not. In the case of 'NO', a driving frequency of the line pressure solenoid 23 is set to a first driving frequency of a comparatively high frequency. In the case of 'YES', the driving frequency of the line pressure solenoid 23 is set to a second driving frequency of a comparatively low frequency. |
