Patent Application
20200400164
The disclosure relates to a fluid powered actuator having a piston reciprocally positioned to move to three different positions. In particular, the present disclosure is directed to a fluid powered actuator which will reciprocate the piston proportionally to the applied fluid pressure.
Various types of fluid actuators are utilized for moving various types of machinery from one position to another position. These actuators utilize fluid to force a piston within a bore to move a shaft and may be either hydraulic or pneumatic. In one type of actuator, fluid pressure is directed to either side of the piston within a fluid tight cylinder to move the piston between positions. Three position actuators are known, such as Assignee's own actuator shown in U.S. Pat. No. 3,991,661.
Oftentimes, actuators are attached to the end of a hydraulic valve spool to raise or lower equipment such as a dump bed of a trailer or to extend or retract a hydraulic cylinder on various types of equipment. The actuator may be attached to the spool of the hydraulic valves. Therefore, an effective area in a fluid chamber on the spool side is less than an effective area in the opposite chamber by same amount as the area of the spool. As a result, response of the piston movement to the applied pressure is different in extend and retract directions.
Embodiments of the present disclosure provide a fluid powered actuator that will respond proportionally to an applied fluid pressure. The fluid actuator includes a piston that is reciprocally positioned within a cylindrical chamber of a body of the actuator. The piston has a channel formed on its external circumferential surface. An O-ring or other seal mechanism resides in the channel to engage an interior wall of the cylindrical chamber and to form a fluid tight seal therewith. The piston includes an axial opening through which a piston shaft passes.
The piston shaft includes multiple steps, an O-ring groove, and a snap ring groove on its surface. The piston shaft passes through a flange bushing and piston while compressing a spring in between them. The piston is held on the piston shaft by the means of the snap ring. The piston shaft is passed through another flange bushing for compressing another spring in between the piston and second flange bushing. The second flange bushing is stopped at the end of the piston shaft. The force of the compression springs on the both sides of the piston will urge the piston to a center position.
The cylindrical chamber forms a fluid tight chamber that may be pressurized. Fluid to the cylindrical chamber is delivered by one of two fluid passageways, i.e., a first fluid passageway and a second fluid passageway. Spring rates and initial compression of the springs are calculated based on the area of the piston, the area of the spool and required working ranges of the fluid pressure. For purposes of this application, “neutral positioning force” is defined as a minimum force required to return the actuator to the neutral position and provide positive holding force to maintain the neutral position when no control fluid pressure is present. Actuator springs are pre-loaded to forces greater than or equal to the desired neutral positioning force. The design described has springs on opposing sides of the piston, but the springs are never at a condition of force equilibrium. The following calculations may be used to determine the required spring rate and initial compression:
Let the area of the piston be Ap and Area of the spool be As. Let the spring rate of a first spring in a first chamber be K1 and that of a second spring in a second chamber be K2. Let the drag force due to the O-rings be Fd. Let the stroke of the actuator be S, fluid pressure in the first chamber is P1 and fluid pressure in the second chamber is P2. Preload in the first spring be PL1 and preload in the second spring is PL2.
The area of the fluid pressure application in the first chamber is A1=Ap.
The area of the fluid pressure application in the second chamber is A2=Ap−As.
The free body diagram of
The free body diagram of
The free body diagram of
The free body diagram of
From the above free body diagrams, we get the starting pressure P1S and ending pressure PIE when pressure is applied in the first chamber for a given stroke S are as follows.
P
1S=(PL2+Fd)/A1;
P
IE=(PL2+Fd+K2S)/A1;
From the above free body diagrams, we get the starting pressure P2S and ending pressure P2E when pressure is applied in the second chamber for a given stroke S as follows.
P
2S=(PL1+Fd)/A2;
P
2E=(PL1+Fd+K1S)/A2;
Since A1>A2, the preloads and spring rates of the springs must be adjusted to make the actuator work in the required pressure ranges.
For purposes of this application, a “proportional positioning actuator” is an actuator wherein fluid pressure is applied to a double acting piston that generates a force acting against a spring, which results in a linear displacement that is proportional to the control fluid pressure.
The design described allows for wider control pressure range and greater ability to configure the minimum pressure at which the actuator begins to move from neutral and the pressure at which the actuator is at maximum displacement.
The actuator of the invention having a piston with only one response to the applied fluid pressure in either directions (extend or retract). This actuator can ensure more precise control of the equipment such as dump bed or hydraulic cylinder.
It is a further object and purpose of the present disclosure to provide a fluid actuator having a piston that can be held at a position in the range of its travel to ensure different flow rates in the hydraulic valves.
It is a further object and purpose of the present disclosure to provide a fluid actuator comprised of readily available components that is simple to assemble and install.
Referring now to
Piston shaft 30 is received in bore 22. Referring now primarily to
Piston shaft 30 defines snap ring groove 50 on central portion 38 between first step 44 and second step 46. Snap ring 52 (
Piston shaft 30 further defines O-ring groove 54 on central portion 38 between snap ring groove 50 and third step 48.
Piston member 60 has a piston cylinder 62 and piston disk 64. Piston cylinder 62 surrounds piston shaft 30. Piston cylinder 62 has first end 66, second end 68, and inside surface 70. Second end 68 abuts third step 48 of piston shaft 30. First end 66 is adjacent snap ring 52 for retaining piston cylinder 62 on piston shaft 30. Piston disk 64 is positioned between first fluid passageway 18 and second fluid passageway 20. Piston disk 64 has a first side 72, a second side 74, and an external circumference defining channel 78. O-ring 80 is located in O-ring groove 54 of piston shaft 30. O-ring 80 is in sealing engagement with inside surface 70 of piston cylinder 62. Seal 82 is located in channel 78 of piston disk 64. Seal 82 is providing sealing engagement with interior wall 24 of bore 22.
Fluid pressure supply switch 90 is provided for selectively routing fluid from forward pressure supply 91 to first fluid passageway 18 and second fluid passageway 20 for selectively moving piston member 60 longitudinally within bore 22 of body 12.
A first flange bushing 100 defines an open end 102 and a closed end 104. Closed end 104 defines first inside surface 106 and first orifice 108 for receiving third portion 38 of piston shaft 30. Open end 102 defines first collar 110 having first end surface 112 and first spring receiving surface 114.
Second flange bushing 120 defines open end 122 and closed end 124. Closed end 124 defines second inside surface 126 and second orifice 128 for receiving central portion 40 of piston shaft 30. Open end 122 defines a second collar 130 having a second end surface 132 and second spring receiving surface 134.
Referring to
Second spring 150 has first end 152 and second end 154. First end 152 abuts second side 74 of piston disk 64. Second end 154 abuts second spring receiving surface 134 of second flange bushing 120.
First securing nut 160 is received on threaded portion 36 of piston shaft 30. First securing nut 160 abuts first step 44 and is adjacent to first inside surface 106 of closed end 104 of first flange bushing 100.
Valve spool 170 has a first end 172 and a second end 174. Second end 174 defines internal threads 176 for receiving threaded portion 36 of piston shaft 30.
First seal ring 180 is adjacent first end 14 of body 12. First seal ring 180 is received within bore 22 of body 12. First seal ring 180 has inside surface 182. Inside surface 182 is for limiting travel of first flange bushing 100 by abutting against first end surface 112 of first flange bushing 100 when first spring 140 is at maximum compression.
First chamber 190 is defined by inside surface 182 of first seal ring 180, interior wall 24 of bore 22 and by first side 72 of piston disk 64.
Second chamber 200 is defined by interior surface 28 of end wall 26 of second end 16 of body 12, interior wall 24 of bore 22 and by second side 74 of piston disk 64.
First area of pressure application 210 is defined by (Area of piston disk 64)−(Area of the spool 170) and is located within first chamber 190.
Second area of pressure application 220 is defined by Area of piston disk 64 and is located within second chamber 200.
First area of pressure application 210 in first chamber 190 is less than second area of pressure application 220 in second chamber 200.
A preload and spring rate of first spring 140 is different than a preload and spring rate of second spring 150 for compensating for a difference between first area of pressure application 210 and second area of pressure application 220.
Embodiments of the present disclosure are well adapted to carry out the objectives and attain the ends and advantages mentioned above as well as those inherent therein. While presently preferred embodiments have been described for purposes of this disclosure, numerous changes and modifications will be apparent to those of ordinary skill in the art. Such changes and modifications are encompassed within the spirit of this disclosure as defined by the claims.
This application claims priority to U.S. Provisional Application No. 62/865,547, filed Jun. 24, 2019, the entire application is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62865547 | Jun 2019 | US |
