Single bushing supported pneumatic actuators
A pneumatic actuator can include a housing and an actuator shaft disposed within the housing and configured to actuate between a first position and a second position. The pneumatic actuator can include a single bushing located within the housing between the housing and the actuator shaft. The single bushing can be configured to support the actuator shaft without the actuator shaft being supported at a second location while allowing actuator motion under set operating conditions.
1. A pneumatic actuator, comprising:
a housing forming both a crank cavity and an actuator cavity;
an actuator shaft disposed within the housing and configured to actuate between a first position and a second position;
a bushing located within the housing between the housing and the actuator shaft, wherein the bushing is between the crank cavity and the actuator cavity, and wherein the bushing is configured to support the actuator shaft without the actuator shaft being supported at a second location while allowing actuator motion under set operating conditions, wherein the bushing comprises a length to diameter ratio greater than 1;
a shaft seal between the housing and the actuator shaft, wherein the shaft seal is between the crank cavity and the actuator cavity;
a pneumatic cup connected to a first end of the actuator shaft, wherein the pneumatic cup is within the actuator cavity; and
a drive connection assembly connected to a second end of the actuator shaft, wherein the drive connection assembly is within the crank cavity.
2. The actuator of claim 1 , wherein the actuator shaft includes a pneumatic cup at a first end, and a drive connection assembly at a second end.
3. The actuator of claim 2 , wherein the length to diameter ratio is between 2 and 3.
4. The actuator of claim 3 , wherein an inner diameter of the bushing is the same or about the same as an outer diameter of the actuator shaft.
5. The actuator of claim 4 , wherein the bushing has a length of about a third of the shaft length.
6. The actuator of claim 5 , further comprising a slotted crank assembly having a slot and connected to the connection assembly at the slot.
7. The actuator of claim 6 , wherein a length of an inner diameter of the bushing that contacts the actuator shaft defined by x 2 −x 1 , solved for using the actuator force equation:
F
ACT
=
F
CR
(
x
1
+
μ
1
D
1
2
)
(
μ
2
cos
α
-
sin
α
)
+
(
x
2
+
μ
2
D
2
2
)
(
sin
α
+
μ
1
cos
α
)
x
2
+
μ
2
D
2
2
-
x
1
-
μ
1
D
1
2
where F ACT is actuator force, wherein For is crank force, μ 1 is a first friction coefficient of the bushing, μ 2 is a second friction coefficient of the bushing, D 1 is a first inner diameter of the bushing, D 2 is a second inner diameter of the bushing, a is the crank angle, x 1 is a distance from a crank point to a first contact point, and x 2 is a distance from a crank point to a second contact point.
8. The actuator of claim 7 , wherein the actuator force F ACT is constrained to be within an operating force range of the actuator shaft, μ 1 =μ 2 , and D 1 =D 2 which equal an outer diameter of the actuator shaft, such that x 2 −x 1 is determinable to result in actuator shaft motion in operation.
9. An aircraft pneumatic system, comprising:
a pneumatic actuator, comprising:
a housing forming both a crank cavity and an actuator cavity;
an actuator shaft disposed within the housing and configured to actuate between a first position and a second position;
a bushing located within the housing between the housing and the actuator shaft, wherein the bushing is between the crank cavity and the actuator cavity, wherein the bushing is configured to support the actuator shaft without the actuator shaft being supported at a second location while allowing actuator motion under set operating conditions, and wherein the bushing has a length to diameter ratio greater than 1; and
a shaft seal between the housing and the actuator shaft, wherein the shaft seal is between the crank cavity and the actuator cavity.
10. The actuator of claim 9 , wherein the actuator shaft includes a pneumatic cup at a first end of the actuator shaft and within the actuator cavity, and a drive connection assembly at a second end of the actuator shaft and within the crank cavity.
11. The actuator of claim 10 , wherein the bushing includes a length to diameter ratio of greater than 1.
12. The actuator of claim 11 , wherein the length to diameter ratio is between 2 and 3.
13. The actuator of claim 12 , wherein an inner diameter of the bushing is the same or about the same as an outer diameter of the actuator shaft.
14. The actuator of claim 13 , wherein the bushing has a length of about a third of the shaft length.
15. The actuator of claim 14 , further comprising a slotted crank assembly having a slot and connected to the connection assembly at the slot.
16. The actuator of claim 15 , wherein a length of an inner diameter of the bushing that contacts the actuator shaft defined by x 2 −x 1 , solved for using the actuator force equation:
F
ACT
=
F
CR
(
x
1
+
μ
1
D
1
2
)
(
μ
2
cos
α
-
sin
α
)
+
(
x
2
+
μ
2
D
2
2
)
(
sin
α
+
μ
1
cos
α
)
x
2
+
μ
2
D
2
2
-
x
1
-
μ
1
D
1
2
where F ACT is actuator force, wherein Fcr is crank force, μ 1 is a first friction coefficient of the bushing, μ 2 is a second friction coefficient of the bushing, D 1 is a first inner diameter of the bushing, D 2 is a second inner diameter of the bushing, a is the crank angle, x 1 is a distance from a crank point to a first contact point, and x 2 is a distance from a crank point to a second contact point.
17. The actuator of claim 16 , wherein the actuator force F ACT is constrained to be within an operating force range of the actuator shaft, μ 1 =μ 2 , and D 1 =D 2 which equal an outer diameter of the actuator shaft, such that x 2 −x 1 is determinable to result in actuator shaft motion in operation.
18. A pneumatic actuator, comprising:
a housing comprising:
a crank cavity;
an actuator cavity;
a partition wall between the crank cavity and the actuator cavity; and
a support tube formed on the partition wall and extending from the partition wall into the actuator cavity;
an actuator shaft disposed within the housing and extending from the actuator cavity to the crank cavity through the support tube, wherein the actuator shaft comprises:
a pneumatic cup at a first end of the actuator shaft, wherein the pneumatic cup is in the actuator cavity; and
a drive connection assembly at a second end of the actuator shaft, wherein the drive connection assembly is in the crank cavity;
a bushing located within the support tube and between the actuator shaft and the support tube, and wherein the bushing comprises a length to diameter ratio greater than 1.
19. The pneumatic actuator of claim 18 , further comprising:
a shaft seal between the actuator shaft and the support tube of the housing, and
wherein the shaft seal is between the crank cavity and the actuator cavity.