| 摘要 |
<p>HYDRAULIC SYSTEM WITH PROPORTIONAL CONTROL An hydraulic control system is disclosed for energizing a load, such as the lift cylinder of an electric lift truck, with a minimum of power loss during the transition from zero to full energization, i.e. during the feathering range. An electric motor drives a positive displacement pump which supplies the flow requirements of different load circuits, one having a greater flow requirement than the other and requiring higher pump speed. A proportioning valve of the open center type provides full flow to the tank when the valve is closed and full flow to the load circuit having the greater flow requirement when the valve is open. A manually actuable lever actuates the valve through the feathering range with the pump motor in a low speed range and actuates a speed control switch to operate the motor in the high speed range when the valve is fully open.</p> |
