SPECIFICATIONValve assemblyThis invention relates to a valve assembly. The invention finds particular application in the retardation of hydraulic motors with mechanical brakes.
Such a valve assembly may be used in hydraulic winches as well as in connection with forward and rotary propulsion of hydraulic excavators and cranes and the drive of hydraulic fork lifts.
The previously known valve assemblies of this type include balance brake valves, backpressure valves and a throttled backpressure valve with adjustable throttling.
There is a drawback to the previously known valve devices of the above type due to the difficulty of establishing a proper synchronization between the hydraulic and the mechanical retardation. A further disadvantage of these previous valve devices is caused by the difficulty of achieving a smooth and calm retarding function. Still another disadvantage to the known valve devices is connected with continuous demand for rather frequent and accurate adjustments.
The present invention seeks to provide a valve assembly especially for retardation of hydraulic motors having a mechanical brake, wherein the above disadvantages are reduced or obviated.
According to the invention there is provided a fluid valve assembly for the hydraulic retardation of a hydraulic motor having a mechanical brake said assembly being such that in its zero position, i.e.
during standstill of the motor, respective fluid channels are open from a motor control valve to the inlet and outlet sides of the motor and from the outlet side of a pair of balance brake valves through a pair of flow valves to a shifting valve and further to the mechanical brake of said motor; and wherein the flow valve on the outlet side of the motor is adapted to shift its position at the starting of said motor, thereby connecting a fluid conduit from said shifting valve to the inlet side of one of the balance brake valves; said assembly including respective backpressure valves on the inlet and outlet sides of motor for causing oil from the outlet side of motor to pass through the respective ones of said flow valves and said balance brake valves; and wherein said balance brake valves are adapted to control and retard said motor; the arrangement being such that relatively high pressure acting either on the inlet or the outlet side of the motor keeps the mechanical motor brake inactive during motor rotation, whereby the respective one of said active balance brake valves ensures that the lower pressure acting either on the inlet or the outlet side of the motor always will exceed the releasing pressure of the mechanical motor brake, said mechanical motor brake being adapted for acutation in response to discharge of oil from said brake into an oil tank through the shifting valve and the respective one of said flow valves, the latter shifting its position when said motor is retarded hydraulically to a standstill, due to the fact that said flow valves react only to oil flow, not to oil pressure.
In order that the invention may be better understood, an embodiment thereof will now be described by way of example only and with reference to the accompanying drawings in which:Figure 1 is a schematic view of one embodiment of a valve assembly according to the invention; andFigure 2 is a schematic view showing the flow valve of Figure 1 in the open position.
Referring to the drawings, a hydraulic motor 1 is connected to an oil pump 2 associated with an oil tank 3. A first side of motor 1 communicates through a control valve 4, oil conduit 5; backpressure valve 6 and oil conduit 7. When control valve 4 is in its zero position, communication is open between oil conduits 5 and 8 respectively and oil tank 3. Oil pump 2 is connected to a second side of the motor 1 through control valve 4, oil conduit 8, backpressure valve 9 and oil conduit 10. A parallel coupling system comprising an oil conduit 11, balance brake valve 12, oil conduit 13, flow valve 14 and oil conduit 15 is inserted between oil conduits 5 and 7 respectively. A parallel coupling system comprising an oil conduit 16, balance brake valve 17, oil conduit 18, flow valve 19 and oil conduit 20 is inserted between oil conduits 8 and 10 respectively.Flow valve 14 has a first side communicating with oil conduit 5 through an oil conduit 21, and a second side communicating with a shifting valve 22 through an oil conduit 23. Flow valve 19 has a first sidle communicating with oil conduit 8 through the oil conduit 24, and a second side communicating with the shifting valve 22 through an oil conduit 25.
Shifting valve 22 is connected to a mechanical brake 26 of the motor 1 through an oil conduit 27. For controlling purposes the balance brake valve 12 is connected to oil conduit 8 through an oil conduit 28.
For the same reason balance brake valve 17 is connected to oil conduit 5 through an oil conduit 29.
The operation of the above described valve assembly will now be explained.
Upon starting of oil motor 1, the motor rotating in a direction as shown by the arrow in Figure 1, control valve 4 is shifted from its zero position to a position allowing oil to flow through oil conduit 5, backpressure valve 6 and oil conduit 7 to motor 1. Thus, an equal pressure is acting on the inlet and outlet sides of balance brake valve 12 and flow valve 14 and on oil conduits 5 and 7 respectively. Upon starting the motor 1 the mechanical brake 26 receives a sufficient amount of oil to loosen the brake through oil conduit 21, flow valve 14, oil conduit 23, shifting valve 22 and oil conduit 27. Balance brake valve 17 receives pressurized oil from oil conduit 5 via oil conduit 29, and is opened for communication between oil conduits 18 and 16 respectively.Thereby an oil flow is established through flow valve 19, thereby causing this valve to shift its position, as will appear fromFigure 2. During rotation of motor 1 in the direction ofarrow, oil from the outlet side of the motor flows through the oil conduit 10. The presence of backpressure valve 9 causes oil to pass through oil conduit 20 to flow valve 19. Hence, oil is led through oil conduit 18, balance brake valve 17, oil conduits 16 and 8 respectively, control valve 4 and back to the oil tank 3.
To achieve retardation of oil motor 1, assuming rotation of motor in the direction of the arrow, control valve 4 is set in its zero position again. This causes oil from conduits 5 and 8 to be discharged into the tank 3. Simultaneously balance brake valve 17 loses its control pressure through oil conduit 29, and starts closing the passage between oil conduits 18 and 16 respectively, thereby narrowing the passage till the pressure in oil conduit 18 equals the predetermined working and shock pressure of the balance brake valve 17. This same pressure is transmitted through flow valve 19 and oil conduits 20 and 10 respectively to the outlet side of motor 1.
Thereby the motor is caused to slow down. During retardation, the pressure acting on the outlet side of motor 1 exceeds that on the inlet side, thereby causing shifting valve 22 to change its position as a result of the fluid pressure in oil conduit 25 being at the same level as the pressure in oil conduits 10 and 20 respectively. (Figure 2), while that in oil conduit 23 is equal to that of the oil conduits 5 and 7. Thus the shifting valve 22 opens, thereby establishing communication between oil conduits 25 and 27, leading to the mechanical brake 26. Thus, during the whole period of retardation, mechanical brake 26 is subjected to a pressure equal to that on the outlet side of motor 1, which prevents actuation of brake 26, as the lower pressure acting either on the inlet or outlet side of the motor 1 always exceeds the releasing pressure of the mechanical brake.
Afterthe motor has been hydraulically slowed down to a total standstill, the balance brake valve 17 will close the connection between oil conduits 18 and 16. This causes the oil flow passing through flow valve 19 to be blocked, whereby the valve changes its position to that shown in Figure 1. In this position communication is established between oil conduits 25 and 24, whereby the mechanical brake 26 is drained into tank 3 through oil conduit 27, shifting valve 22, oil conduit 25, flow valve 19, oil conduits 24 and 8 and control valve 4. After the motor 1 has stopped if the shifting valve should for some reason change position, communication will be open for discharge of oil from the mechanical brake 26 into the oil tank 3 through oil conduit 23, flow valve 14, oil conduits 21 and 5 and control valve 4.Such discharge will cause actuation of the mechanical brake 26.
It will be readily appreciated that the symmetric construction of the valve assembly described above allows rotation and retardation of the motor 1 in an opposite direction to that indicated by the arrow, in the same way as described above.
The valve assembly will prevent actuation of mechanical brake 26 during rotational motion of motor 1. Due to this fact brake 26 may be designed exciusivelyforthe purpose of locking the stationary motor 1 in position, after the motor has been slowed down hydraulically to a total standstill.
An advantage of the valve assembly described above is that the mechanical brake 26 works quietly.
Furthermore, the braking moment will remain constant during the whole period of retardation.
Another advantage of the described apparatus is that, after the working and shock pressure of the balance brake valves 12 and 17 has been preset, no further adjustment will be necessary.
It is clear that the valve assembly described above may be utilized for other purposes than the above.
For example, the valve assembly is suitable for use in association with a piston moving in a hydraulic cylinder, for providing a signal causing a change of function when the stream of oil flowing to or from the hydraulic cylinder, is cut off.