Cylinder Friction (TL)

Piston friction in a hydraulic cylinder in a thermal liquid network.

cylinder friction tl

Description

The Cylinder Friction (TL) block simulates the friction of a piston in a hydraulic cylinder in a network of thermal liquid. The total friction is a combination of Stribeck, Coulomb and viscosity effects. The Coulomb component of friction includes the effect of the initial force created by the seal and the effect of the pressure in the cylinder.

The block calculates the Stribeck and viscous forces using the same approach as the block Translational Friction

Stribeck and viscous friction forces

The Stribeck friction force is the dominant component of friction at low speeds. This block uses Eq:

where

- value of parameters Breakaway to Coulomb friction force ratio, ;
- cylinder piston displacement speed, ;
- static torque threshold velocity:

where is the value of the Breakaway friction velocity parameters. The block sets the transition range from 0 to the static torque threshold velocity to ensure smooth modelling of the friction force;
- dry (Coulomb) friction.

The viscous friction force depends on the value of the Viscous friction coefficient parameters, , and is proportional to the piston speed:

Coulomb friction force

The Coulomb frictional force is a force directed perpendicular to the friction surface. The motion of the piston creates a radial stress within the stationary cylinder body, which increases as the internal fluid in the cylinder is compressed. The radial stress is normal to the direction of piston motion and results in a Coulomb friction force that opposes piston motion.

The Coulomb friction force has the form:

where

- is the relative speed between ports R and C, ;
- threshold velocity for the Coulomb force, .

The threshold velocity for the Coulomb force is not the same as the threshold velocity for the static force that the block uses to calculate the Stribeck friction force, although they both act as a threshold region to ensure smooth modelling of the Coulomb force and the Stribeck force.

- force contribution from seal preloading and cylinder pressure,

where

- is the value of the Preload force parameters;
- is the value of the Coulomb friction force coefficient parameters;
and are the pressures at the cylinder ports A and B respectively. These values are overpressures relative to ambient pressure and are defined in terms of atmospheric or other user-defined pressures using the Environment pressure specification parameters.

Ports

Conserving

# A — thermal liquid port
thermal liquid

Details

The thermal liquid port corresponds to the input or output. This unit has no internal directionality.

Program usage name

port_a

# C — mechanical port
translational mechanics

Details

A mechanical progressive port corresponding to a body, that is, a stationary body.

Program usage name

case_flange

# B — thermal liquid port
thermal liquid

Details

The thermal liquid port corresponds to the input or output. This unit has no internal directionality.

Program usage name

port_b

# R — mechanical port
translational mechanics

Details

A mechanical progressive port corresponding to a rod, that is, a moving body.

Program usage name

rod_flange

Parameters

# Same fluid on both sides — option to simulate the same fluid on both sides of the block

Details

Whether the same fluid is modelled on both sides of the block. If the parameters are checked, the fluid properties are propagated through the block. If unchecked, the chambers in the block are connected to isolated networks of fluids with different properties.

Default value	`true (switched on)`
Program usage name	`same_properties`
Evaluatable	No

# Breakaway to Coulomb friction force ratio — the ratio of the detachment force to the Coulomb friction force

Details

Ratio of detachment force to Coulomb friction force .

Default value	`1.2`
Program usage name	`Coulomb_breakaway_ratio`
Evaluatable	Yes

# Breakaway friction velocity — friction threshold
fpm | fps | kph | mph | m/s | cm/s | ft/s | in/s | km/s | mi/s | mm/s

Details

Threshold value for movement against friction force.

Values	`fpm` \| `fps` \| `kph` \| `mph` \| `m/s` \| `cm/s` \| `ft/s` \| `in/s` \| `km/s` \| `mi/s` \| `mm/s`
Default value	`0.1 m/s`
Program usage name	`v_breakaway`
Evaluatable	Yes

# Preload force — initial force in the cylinder arising during seal assembly
N | kN | lb | mN | dyn | lbf

Details

The initial force in the cylinder due to the seal assembly. The unit uses this parameter to calculate the Coulomb friction force.

Values	`N` \| `kN` \| `lb` \| `mN` \| `dyn` \| `lbf`
Default value	`20.0 N`
Program usage name	`F_preload`
Evaluatable	Yes

# Coulomb friction force coefficient — Coulomb friction force coefficient
m^2 | cm^2 | ft^2 | in^2 | km^2 | mi^2 | mm^2 | um^2 | yd^2 | N/Pa

Details

Coulomb friction force coefficient. The block uses this parameters to calculate the Coulomb friction force.

Values	`m^2` \| `cm^2` \| `ft^2` \| `in^2` \| `km^2` \| `mi^2` \| `mm^2` \| `um^2` \| `yd^2` \| `N/Pa`
Default value	`1e-6 N/Pa`
Program usage name	`Coulomb_coefficient`
Evaluatable	Yes

# Viscous friction coefficient — viscous friction coefficient
kg/s | N*s/m | N/(m/s) | lbf/(ft/s) | lbf/(in/s)

Details

Coefficient of viscous friction. This parameter is used to calculate the viscous friction force.

Values	`kg/s` \| `N*s/m` \| `N/(m/s)` \| `lbf/(ft/s)` \| `lbf/(in/s)`
Default value	`100.0 N/(m/s)`
Program usage name	`viscous_coefficient`
Evaluatable	Yes

# Environment pressure specification — ambient pressure setting method
Atmospheric pressure | Specified pressure

Details

Specifies the ambient pressure reference method for calculating Coulomb friction:

Atmospheric pressure - atmospheric pressure.
Specified pressure - the exact value specified in the Environment pressure parameters.

Values	`Atmospheric pressure` \| `Specified pressure`
Default value	`Atmospheric pressure`
Program usage name	`pressure_type`
Evaluatable	No

# Environment pressure — ambient pressure
Pa | GPa | MPa | atm | bar | kPa | ksi | psi | uPa | kbar

Details

User-defined pressure value for calculating Coulomb friction.

Dependencies

Available when the Environment pressure specification parameters are set to Specified pressure.

Values	`Pa` \| `GPa` \| `MPa` \| `atm` \| `bar` \| `kPa` \| `ksi` \| `psi` \| `uPa` \| `kbar`
Default value	`0.101325 MPa`
Program usage name	`p_specified`
Evaluatable	Yes