| 摘要 |
<p>A fluid controller (17) is disclosed for controlling the flow of fluid to a steering cylinder (19). The controller includes a fluid meter (51) and a valving arrangement (49) including a valve spool (65) and a sleeve (67), which define a main fluid path including a main variable flow control orifice (121), the fluid meter (51), a variable flow control orifice (123), the steering cylinder (19), and a variable flow control orifice (125). In accordance with the invention, the spool and sleeve define an amplification fluid path including a variable amplification orifice (129) in parallel with the main fluid path, and disposed to amplify the flow of fluid through the meter. In one embodiment of the invention, the amplification fluid path communicates with the main fluid path upstream of the main variable flow control orifice, and at a location downstream of the fluid meter, but upstream of the variable flow control orifice (123). In order to facilitate manual steering using the fluid controller of the invention, the amplification orifice (129) reaches its maximum flow area when the spool and sleeve are still several degrees away from their maximum displacement. The amplification orifice then decreases and closes as the spool and sleeve reach maximum displacement. As a result, the amplification fluid path is closed at maximum valve displacement, and therefore does not act as a short-circuit, making it impossible to manually steer.</p> |
