Servo system method and apparatus, servo valve apparatus therefor and method of making same

Claim 1

Apparatus comprising: a housing defining an inlet port, an outlet port, a vent port, and a flow path communicating each port with the others; a pair of relatively movable valve members movably received by said housing, a first of said pair of valve members sealingly cooperating with said housing in a first position to close fluid communication between said inlet port and said outlet port, said first valve member moving to a second position opening fluid communication between said inlet port and said outlet port; the second of said pair of valve members in a first position sealingly cooperating with said first valve member to close fluid communication between said outlet port and said vent port, said second valve member moving to a second position opening communication between said outlet port and said vent port; means for moving either selected one of said pair of valve members respectively to said second position thereof; means for urging said selected one of said pair of valve members toward the respective first position thereof substantially as a first time derivative of fluid pressure at said outlet port; output means for moving an output member in a first direction in response to flow of pressure fluid from said output means via said outlet port and vent port, and in a second direction opposite said first direction in response to flow of pressure fluid from a source thereof to said output means via said inlet port and outlet port; said output means further comprising means defining a first movable pressure-responsive surface continuously communicating with pressure fluid at said inlet port and having a first respective product of effective area and mechanical advantage to urge said output member in said first direction of movement, and means defining a second movable pressure-responsive surface communicating with pressure fluid at said outlet port and having a second respective product of effective area and mechanical advantage exceeding said first product to urge said output member in said second direction opposite said first direction, a determined fluid pressure differential between said first pressure responsive surface and said second pressure responsive surface effecting equilibrium without movement of said output member, and effective fluid pressure differentials other than said determined differential effecting acceleration of said output member substantially proportional to the difference between said determined differential and the effective pressure differential, whereby said urging of said selected one of said pair of valve members toward the respective first position thereof by said means therefor is analogous with acceleration of said output member.