Steering control unit with flow amplification

A controller operable to control the flow of fluid from a source of pressurized fluid to a fluid pressure operated device;

• said controller being of the type including housing means defining an inlet port for connection to the source of pressurized fluid, a return port for connection to a reservoir, and first and second control fluid ports for connection to the fluid pressure operated device;
• valve means disposed in said housing means and defining a neutral position and a first operating position;
• said housing means and said valve means cooperating to define a main fluid path communicating between said inlet port and said first control fluid port, and between said second control fluid port and said return port when said valve mean is in said first operating position;
• fluid actuated means for imparting follow-up movement to said valve means proportional to the volume of fluid flow through said fluid actuated means said fluid actuated means being disposed in series flow relationship in said main fluid path between said inlet port and said first control fluid port;
• said main fluid path including first and second variable flow control orifices disposed in series flow relationship between said inlet port and said fluid actuated means, each having its minimum flow area when said valve means is in said neutral position, and an increasing flow area as said valve means is displaced from said neutral position toward said first operating position;
• said main fluid path including third and fourth variable flow control orifices disposed between said fluid actuated means and said first control fluid port;
• characterized by:
• (a) said housing means and said valve means cooperating to define an amplification fluid path, in parallel with said main fluid path, said amplification fluid path being in fluid communication with said main fluid path at a first location disposed between said first and second variable flow control orifices, and at a second location disposed between said fluid actuated means and said first control fluid port;
• (b) said amplification fluid path including a variable amplification orifice having its minimum flow area when said valve means is in said neutral position, and an increasing flow area as said valve means is displaced from said neutral position toward said first operating position;
• and
• (c) said main variable flow control orifice begins to open at least as soon as said variable amplification orifice, as said valve means moves from said neutral position toward said first operating position.