| 摘要 |
<p>The neutral override circuit of this invention includes a variable displacement pump (12) controlled by a servo (56) fluidly connected to a displacement control (70) that is biased to a neutral position. A charge pump (58) is connected to the pump and the displacement control. A solenoid-operated neutral override brake control valve (20) is connected to the charge circuit upstream of the displacement control valve and is normally biased to an open position. However, the solenoid (50) urges the valve to a closed position in a response to a signal indicating that the brake has been released. In the open position, the valve dumps charge flow to the pump case (74) until the supply pressure to the displacement control is inadequate to overcome the centering bias of the displacement control. The characteristics of the brake control valve can be set so that some minimum charge pressure and lubricating flow are still provided to the rotating elements of the pump.</p> |
