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1. WO2012054969 - A NEW MECHANISM FOR FLUID POWER TRANSMISSION AND CONTROL

Note: Text based on automatic Optical Character Recognition processes. Please use the PDF version for legal matters

[ EN ]

A New Mechanism for Fluid-Power Transmission and Control

The rotary valves in Fluid Power Transmission and Control normally operate in two ways. One just combines a traditional spool valve with a mechanical screw device, transforming rotary motion into axial motion, and the other uses longitudinal grooves on the surface of a spool to switch the connection/distribution between different ports. These two fluid-power transmission and control mechanisms are complicated to manufacture and have low frequency reactions.

This invention introduces a new concept for rotary valves used in fluid power transmission and control. It transforms the rotary motion precisely to axial straight motion. It can also be used as an actuator.

Before explaining the details of this invention, some symbols need to be defined:

P: The fluid power inlet port (high pressure)

T: The port that connects to the tank or the reservoir line (low pressure)

In order to demonstrate the main functions clearly, other structural details such as spool lands, seals, centering springs, etc. are out of consideration.

Figure (1) shows the simplified cross section of this mechanism. There are two sensitive chambers at the ends: C1 and C2. The fluid pressure in C1 acts on the spool in area A1, and the fluid pressure in C2 acts on the spool in area A2. A1 is larger than the annular area of A2. Four helical grooves operate in axial symmetry; two of them connect C1, while the others connect C2. On the surface of the bore, the two ports P and two ports T get covered by the helical teeth as they, too, operate in axial symmetry. The fluid pressure in C1 is P1, and the fluid pressure in C2 is P2. The axial force caused by fluid pressure acts on the spool in C1 (A1xP1) tends to push the spool rightwards, and the axial force caused by fluid pressure in C2 (A2xP2) tends to push the spool leftwards, creating a balanced state:

P1xA1 = P2xA2

Figure (2) shows the connection of ports after the spool rotates in an anti-clockwise direction. The rotary motion of the helical groove makes the port P open the channel to C1, increasing the fluid pressure PI. Meanwhile, C2 connects to port T, decreasing the fluid pressure P2, so, P1xA1 > P2xA2, forcing the spool rightwards. This rightwards slide motion of the spool forces the helical teeth to gradually block ports P and T until the fluid pressure in the chambers reverts to the balanced state, P1xA1 = P2xA2.

Figure (3) demonstrates balanced state. The spool has moved a distance rightwards.

Figure (4) shows the connections of the ports after the spool rotates in a clockwise angle. C1 connects to port T, decreasing the fluid pressure P1. Meanwhile, C2 connects to port P, increasing the fluid pressure P2. Thus P1xA1 < P2xA2, forcing the spool to move leftwards. This leftwards slide motion of the spool forces the helical teeth to gradually block ports P and T until the fluid pressure in the chambers reverts to the balanced state, P1xA1 = P2xA2.

Figure (5) demonstrates the balanced state. The spool has moved a distance leftwards.

Furthermore, in many conditions the chamber with the small area is always connected to a high-pressure port P. This efficiently simplifies the structure.

Figure (6) shows the simplified mechanism. The chamber C2 is always connected to port P, so P2=P. There are only two helical grooves, axial symmetry, connect C1. Fluid pressure in C1 = P1. The fluid pressure acts on the spool in C1 (A1xP1), tending to push the spool rightwards, and the axial force cased by the fluid pressure acts on the spool in C2 (A2xP), tending to push the spool leftwards, creating a balanced state:

P1=PxA2/A1; P1xA1 = PxA2.

Figure (7) shoes the connections of the ports after the spool rotates in an anti-clockwise direction. C1 connects port P, increasing the fluid pressure in C1 (PI), so, P1xA1 > PxA2. The spool is then moved rightwards. The rightwards slide motion of the spool forces the helical teeth to gradually block port P until the fluid pressure in C1 ( P1) is reverted to a balanced state, P1 = PxA2/A1; P1xA1 = PxA2

Figure (8) demonstrates the balanced state. The spool has moved a distance rightwards.

Figure (9) shows the connections of the ports after the spool rotates in a clockwise direction. C1 connects to port T, decreasing the fluid pressure P1, so,

P1xA1 < PxA2. The spool is then moved leftwards. The leftwards slide motion of the spool forces the helical teeth to gradually block port T until the fluid pressure in C1 (P1) is reverted to a balanced state:

PI = PxA2/A1; P1xA1 = PxA2

Figure (10) demonstrates the balanced state. The spool has moved a distance leftwards.

This mechanism can also be transformed to a servo amplifier or a transducer in a closed loop. For example, as shown on figure (11), the spool rotates clockwise as input. The fluid pressure and flow rate are then transmitted out to separate chambers built in other parts. As a result, the fed-back rightwards motion accomplished by other parts acts on the sleeve.

The aforesaid motions are all relative to each other between the spool and the sleeve.

For instance, if the spool rotates anti-clockwise, it may mean that the sleeve rotates clockwise in reality, and vice versa. The straight slide movement is the same.

In conclusion, this invention sets up a pilot function on the main spool and optimally utilises the characteristics of helical grooves.