| 摘要 |
1466605 Fluid-pressure control circuits MASSEY-FERGUSON SERVICES NV 14 Nov 1974 [14 Nov 1973] 49261/74 Heading F1P [Also in Division E1] In a circuit, Fig. 3, in which an auxiliary pump P2 supplies fluid either to a line 3, fed by a main pump P 1 , or to a reservoir 19 under the control of a valve 14, which is changed over in response to a predetermined pressure level in an actuator 10, the circuit controlling changeover of the valve 14 includes a time delay device 13a. The latter prevents changeover occurring in response to transient pressure changes. As described, when the pressure in the actuator 10 reaches a predetermined level a switch 11 closes. The latter is in a circuit which includes the time delay device 13a. If the pressure level is maintained for the length of the delay period a switch 13d is opened by a solenoid 13c. This changes over the valve 16 to the position shown, in which the output of the pump P 2 is returned to the reservoir, from the alternative position in which the output is fed into the line 3. The latter position occurs on closing a switch 51 which is coupled to the engine driving the pumps. When the solenoid 16a is energized the pressure in line 3 is applied to the by-pass valve 14 to close it thereby diverting the output of pump P 2 from the reservoir to line 3. Fig. 4, (not shown), illustrates a circuit in which the solenoid 16a is energized only when one or other of control valves 4a, 4b is feeding fluid to one of rams 9, 10, i.e. fluid from pump P 2 returns to reservoir unless one or other of rams 9, 10 is operating. In Fig. 5 an addition pump P3 supplies steering cylinders 42. A flow divider valve 22a is in the condition shown when the engine is running relatively slowly, the output of pump P3 is therefore low. The circuit is applied to a loader, Fig. 1, (not shown), which will be travelling relatively slowly and will therefore require a high steering rate. The flow from pump P 2 will be diverted to circuit 17b where it will contribute to this. If the engine is running at a high speed a lower actuator 22d will move valve 22a to its centre position and divert the P 2 output to either the steering circuit or to valve 14 whichever offers least resistance. If the engine is running at high speed and there is no steering demand the lower actuator 22d moves valve 22a into a third position in which all the flow from P 2 goes to valve 14.
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