Hydraulic actuators: cylinders Cylinder...

2005/2006 I. Hydraulic and Pneumatic Systems 1

Hydraulic actuators: cylindersCylinder types:

Single acting:

work can be done only in one direction

Piston

Double acting piston:

Piston rod on both sides

Plunger

Work is done in both

directions

Telescopic Telescopic Fast moving

Tandem

Fast moving


Hydraulic cylinders

Hydraulic cylinderHidraulikus munkahengerek

Rögzítőpálcás kivitel 1.

Rögzítőpálcás hidraulika henger, a hengerfejen található karimás rögzítéssel


Hydraulic cylinders

Hydraulic cylinder Hidraulikus munkahengerek

Hengeres kivitel 1.

Hengeres építési móddal készült hidraulika henger


Hydraulic cylinders

Properties:

The cylinders have to be good quality steel with close tolerances.

There have to be good sealing both at the piston rod and at the

cylinder.

With time dirt may come in and damage the surfaces. This has to be

possibly reduced.

In this case, the leakage will increase all the time.


Hydraulic cylinders

Calculation of cylinders

1maxmaxFFFF FLc ++= FLC FFF +≈

maxmax

22110 pApAFC −=

1122 pApAFCB −=

1

0A

Qv =

2A

Qv

B=

friction forces inertial forcesmaximum loadslow motion, can

be often neglected

Backward:

Outward:

Q

A2A1

p1

p2vB

v0


Hydraulic cylinders

Calculation of cylinders

Hydraulic cylinders should be possibly

operated in the 3rd region for smooth

operation.

If the cylinder is new, the leakage losses are

negligibly small so that:

ηc = ηmech

Ff1

v

2 3

1. Stick-slip

2. Transition

3. Normal behaviour

22112211ApAp

F

QpQp

Fv LLc −

=−⋅

=η

92,085,0max

−=cη

ηc

∆p

outwardsinwards

at higher pressures


Hydraulic cylinders

Checking for buckling

n: safety factor: 1-3,5

lk: buckling length

I1: moment of inertia of the piston rod

E: elasticity modulus of the rod material

1

2

max

1IE

lnF

k

L ⋅⋅

=

π

64

4πd

Maximum permissible force:


Hydraulic cylinders

Cushioning of cylinders:

A hard impact of the piston at the end surfaces has to be inhibited

– kinetic energy has to be absorbed.

This is done by increasing the hydraulic resistance at the end of

the stroke.


Rotary hydraulic actuators

Swivel vane rotary actuator:

Limited angle in both directions

Maximum angle always smaller than 360°

The same torque in both directions

Piston rotary actuator:

With rack and gear coupling

Here maximum angle may be larger than 360°Mindkét irányban azonosan

működő hengerrel és fogasléces

meghajtással működtetett

tolódugattyús lengőhajtás

Párhuzamdugattyús

lengőhajtás

Forgódugattyús

lengőhajtás menettel

működtetett meghajtócsappal

Limited angle rotary

actuatorLimited angle rotary

actuator

Parallel

piston rotary

actuator

??? ???


Big pictures

End of normal presentation

Beginning of big pictures


Hydraulic cylinders

Cylinder types: plunger

smaller force, better efficiency, axial support is necessary

but cylinder does not have to be so good quality

Without inner buffer With inner buffer (pilot piston)


Hydraulic cylinders

Cylinder types: piston, single acting, pressing-cylinder

Spring

inside outside


Hydraulic cylinders

Cylinder types: piston, single acting, puller

Spring

inside outside


Hydraulic cylinders

Cylinder types: piston, double acting

Velocity is different


Hydraulic cylinders


Piston rod on both side

Velocity is the same in both directions


Hydraulic cylinders


Piston rod on both side

Velocity is different in the two directions depending on

cross section ratio of the rods


Hydraulic cylinders

Cylinder types: double acting piston, tandem


Hydraulic cylinders

Cylinder types: single acting, fast moving


Hydraulic cylinders

Cylinder types: double acting, fast moving


Hydraulic cylinders

Cylinder types: telescopic, single acting

Large working paths

or limited space


Hydraulic cylinders

Cylinder types: telescopic, double acting

Large working paths

or limited space


Hydraulic cylinders

Checking for buckling:

Euler’s

cases

Picture

Free buckling length

Manner of end fixing

Note

1. Case

One end freeOne end fixed

Or trunnion at end

mounting style mounting style mounting style

2. Case

Two ends pivoted and guided

3. Case

One end guided and pivoted, other end

fixed

4. Case

Two ends fixed and guided

mounting style


Hydraulic cylinders

Cushioning of cylinders:

1. Piston

2. Cushion nose

3. Cylinder cap

4. Stroke volume

5. Cushion orifice

6. Throttle

7. Cushion adjustment screw

8. Mother

9. Non-return valve

10. Gas valve



Parallel piston rotary

actuator



???



Rack-and-pinion piston-type rotary actuator:


Rotary hydraulic actuatorsLimited angle rotary actuator:



Limited angle rotary actuator:



Helix actuator:

Hydraulic actuators: cylinders Cylinder...

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