Power steering apparatus for vehicle

A power steering apparatus for a vehicle comprising:

• a steering mechanism including an input shaft connected to a steering wheel side and an output shaft connected to steered wheels, rotatably supported coaxially in a housing and elastically connected to be rotatable relative to each other, for steering the steered wheels according to steering operation of said steering wheel;
• valve means for controlling supply of a fluid to a power cylinder exerting an assist force on said output shaft according to relative rotation between said input shaft and said output shaft;
• a pressed portion disposed to be projected to at least one side of said input shaft and said output shaft in a radial direction of the shaft;
• a large-diameter portion disposed at least the other side of said input shaft or said output shaft and having a chamber for rotatably containing said pressed portion;
• first and second hydraulic pressure chambers formed independent of each other between said housing and said large-diameter portion;
• a first plunger slidably engaged with a hole formed in said large-diameter portion and opening to said first hydraulic pressure chamber to contact against said pressed portion, for pressing said pressed portion in one direction by a hydraulic pressure applied to said first hydraulic pressure chamber for applying a rotational force to said input shaft or said output shaft;
• a second plunger slidably engaged with a hole formed in said large-diameter portion and opening to said second hydraulic pressure chamber to contact against said pressed portion, for pressing said pressed portion in one direction by a hydraulic pressure applied to said second hydraulic pressure chamber for applying a rotational force to said input shaft or said output shaft;
• first and second annular oil passages connected individually to said first and second hydraulic pressure chambers;
• control valves for controlling hydraulic pressures to said first and second hydraulic pressure chambers for driving said first and second plungers through said first and second annular oil passages;
• and
• a fluid change-over circuit having a fixed mode for driving simultaneously said first and second plungers for regulating rotation of said input shaft or output shaft and a rotation mode for driving one of said first and second plungers for exerting a rotational force on said input shaft or said output shaft, whereby selecting one of said modes according to operation condition of the vehicles.

A power steering apparatus for a vehicle comprising:

• a steering mechanism including an input shaft connected to a steering wheel side and an output shaft connected to steered wheels, rotatably supported coaxially in a housing and elastically connected to be rotatable relative to each other, for steering the steered wheels according to steering operation of said steering wheel;
• valve means for controlling supply of a fluid to a power cylinder exerting an assist force on said output shaft according to relative rotation between said input shaft and said output shaft;
• a pressed portion disposed to be projected to at least one side of said input shaft and said output shaft in a radial direction of the shaft;
• a large-diameter portion disposed at least the other side of said input shaft or said output shaft and having a chamber for rotatably containing said pressed portion;
• first and second hydraulic pressure chambers formed independent of each other between said housing and said large-diameter portion;
• a first plunger slidably engaged with a hole formed in said large-diameter portion and opening to said first hydraulic pressure chamber to contact against said pressed portion, for pressing said pressed portion in one direction by a hydraulic pressure applied to said first hydraulic chamber for applying a rotational force to said input shaft or said output shaft;
• a second plunger slidably engaged with a hole formed in said large-diameter portion and opening to said second hydraulic pressure chamber to contact against said pressed portion, for pressing said pressed portion in one direction by a hydraulic pressure applied to said second hydraulic pressure chamber for applying a rotational force to said input shaft or said output shaft;
• first and second annular oil passages connected individually to said first and second hydraulic pressure chambers;
• control valves for controlling hydraulic pressures to said first and second hydraulic pressure chambers for driving said first and second plungers through said first and second annular oil passages;
• operation condition detection means for detecting operation condition of the vehicle;
• and
• control means for controlling operation of said control valves in response to detection signal detected by said operation condition detection means.