Main Content

Variable-Displacement Motor (IL)

Variable-displacement motor in an isothermal liquid system

  • Library:
  • Simscape / Fluids / Isothermal Liquid / Pumps & Motors

  • Variable-Displacement Motor (IL) block

Description

The Variable-Displacement Motor (IL) block models a motor with variable-volume displacement. The fluid may move from port A to port B, called forward mode, or from port B to port A, called reverse mode. Motor mode operation occurs when there is a pressure drop in the direction of the flow. Pump mode operation occurs when there is a pressure gain in the direction of the flow.

The shaft rotation corresponds to the sign of the fluid volume moving through the motor, which is received as a physical signal at port D. Positive fluid displacement at D corresponds to positive shaft rotation in forward mode. Negative fluid displacement at D corresponds to negative shaft angular velocity in forward mode.

Operation Modes

The block has eight modes of operation. The working mode depends on the pressure drop from port A to port B, Δp = pApB; the angular velocity, ω = ωRωC; and the fluid volumetric displacement at port D. The figure above maps these modes to the octants of a Δp-ω-D chart:

  • Mode 1, Forward Motor: Flow from port A to port B causes a pressure decrease from A to B and a positive shaft angular velocity.

  • Mode 2, Reverse Pump: Negative shaft angular velocity causes a pressure increase from port B to port A and flow from B to port A.

  • Mode 3, Reverse Motor: Flow from port B to port A causes a pressure decrease from B to A and a negative shaft angular velocity.

  • Mode 4, Forward Pump: Positive shaft angular velocity causes a pressure increase from port A to port B and flow from A to B.

  • Mode 5, Reverse Pump: Positive shaft angular velocity causes a pressure increase from port B to port A and flow from B to A.

  • Mode 6, Forward Motor: Flow from port A to port B causes a pressure decrease from A to B and a positive shaft angular velocity.

  • Mode 7, Forward Pump: Negative shaft angular velocity causes a pressure increase from port A to port B and flow from A to B.

  • Mode 8, Reverse Motor: Flow from B to A causes a pressure decrease from B to A and positive shaft angular velocity.

The motor block has analytical, lookup table, and physical signal parameterizations. When using tabulated data or an input signal for parameterization, you can choose to characterize the motor operation based on efficiency or losses.

The threshold parameters Pressure drop threshold for motor-pump transition, Angular velocity threshold for motor-pump transition, and Displacement threshold for motor-pump transition identify regions where numerically smoothed flow transition between the motor operational modes can occur. For the pressure and angular velocity thresholds, choose a transition region that provides some margin for the transition term, but which is small enough relative to the typical motor pressure drop and angular velocity so that it will not impact calculation results. For the displacement threshold, choose a threshold value that is smaller than the typical displacement volume during normal operation.

Analytical Leakage and Friction Parameterization

If you set Leakage and friction parameterization to Analytical, the block calculates internal leakage and shaft friction from constant nominal values of shaft velocity, pressure drop, volumetric displacement, and torque. The leakage flow rate, which is correlated with the pressure differential over the motor, is calculated as:

m˙leak=KρavgΔp,

where:

  • Δp is pApB.

  • ρavg is the average fluid density.

  • K is the Hagen-Poiseuille coefficient for analytical loss,

    K=Dnomωnom(1ηv,nom1)Δpnom,

    where:

    • Dnom is the Nominal displacement.

    • ωnom is the Nominal shaft angular velocity.

    • ηnom is the Volumetric efficiency at nominal conditions.

    • Δpnom is the Nominal pressure drop.

The torque, which is related to the motor pressure differential, is calculated as:

τfr=(τ0+k|ΔpDDnom|)tanh(4ω5×105ωnom),

where:

  • τ0 is the No-load torque.

  • k is the friction torque vs. pressure gain coefficient at nominal displacement, which is determined from the Mechanical efficiency at nominal conditions, ηm,nom:

    k=τfr,nomτ0Δpnom.

    τfr,nom is the friction torque at nominal conditions:

    τfr,nom=(1ηm,nom)DnomΔpnom.

  • Δp is the pressure drop between ports A and B.

  • ω is the relative shaft angular velocity, or ωRωC.

Tabulated Data Parameterizations

When using tabulated data for motor efficiencies or losses, you can provide data for one or more of the motor operational modes. The signs of the tabulated data determine the operational regime of the block. When data is provided for less than eight operational modes, the block calculates the complementing data for the other mode(s) by extending the given data into the remaining octants.

The Tabulated data - volumetric and mechanical efficiencies parameterization

The leakage flow rate is calculated as:

m˙leak=m˙leak,motor(1+α2)+m˙leak,pump(1α2),

where:

  • m˙leak,pump=(ηυ1)m˙ideal

  • m˙leak,motor=(1ηv)m˙

and ηv is the volumetric efficiency, which is interpolated from the user-provided tabulated data. The transition term, α, is

α=tanh(4ΔpΔpthreshold)tanh(4ωωthreshold)tanh(4DDthreshold),

where:

  • Δp is pApB.

  • Δpthreshold is the Pressure drop threshold for motor-pump transition.

  • ω is ωRωC.

  • ωthreshold is the Angular velocity threshold for motor-pump transition.

The torque is calculated as:

τfr=τfr,pump(1+α2)+τfr,motor(1α2),

where:

  • τfr,pump=(ηm1)τ

  • τfr,motor=(1ηm)τideal

and ηm is the mechanical efficiency, which is interpolated from the user-provided tabulated data.

The Tabulated data - volumetric and mechanical losses parameterization

The leakage flow rate is calculated as:

m˙leak=ρavgqloss(Δp,ω,D),

where qloss is interpolated from the Volumetric loss table, q_loss(dp,w,D) parameter, which is based on user-supplied data for pressure drop, shaft angular velocity, and fluid volumetric displacement.

The shaft friction torque is calculated as:

τfr=τloss(Δp,ω,D),

where τloss is interpolated from the Mechanical loss table, torque_loss(dp,w,D) parameter, which is based on user-supplied data for pressure drop, shaft angular velocity, and fluid volumetric displacement.

Input Signal Parameterization

When Leakage and friction parameterization is set toInput signal - volumetric and mechanical efficiencies, ports EV and EM are enabled. The internal leakage and shaft friction are calculated in the same way as the Tabulated data - volumetric and mechanical efficiencies parameterization, except that ηv and ηm are received directly at ports EV and EM, respectively.

When Leakage and friction parameterization is set toInput signal - volumetric and mechanical losses, ports LV and LM are enabled. These ports receive leakage flow and friction torque as positive physical signals. The leakage flow rate is calculated as:

m˙leak=ρavgqLVtanh(4Δppthresh),

where:

  • qLV is the leakage flow received at port LV.

  • pthresh is the Pressure drop threshold for motor-pump transition parameter.

The friction torque is calculated as:

τfr=τLMtanh(4ωωthresh),

where

  • τLM is the friction torque received at port LM.

  • ωthresh is the Angular velocity threshold for motor-pump transition parameter.

The volumetric and mechanical efficiencies range between the user-defined specified minimum and maximum values. Any values lower or higher than this range will take on the minimum and maximum specified values, respectively.

Motor Operation

The motor flow rate is:

m˙=m˙ideal+m˙leak,

where m˙ideal=ρavgDω.

The motor torque is:

τ=τidealτfr,

where τideal=DΔp.

The mechanical power extracted by the motor shaft is:

φmech=τω,

and the motor hydraulic power is:

φhyd=Δpm˙ρavg.

To be notified if the block is operating beyond the supplied tabulated data, you can set Check if operating beyond the octants of supplied tabulated data to Warning to receive a warning if this occurs, or Error to stop the simulation when this occurs. When using input signal for volumetric or mechanical losses, you can be notified if the simulation surpasses operating modes with the Check if operating beyond motor mode parameter.

You can also monitor motor functionality. Set Check if pressures are less than motor minimum pressure to Warning to receive a warning if this occurs, or Error to stop the simulation when this occurs.

Ports

Conserving

expand all

Liquid entry or exit port to the motor.

Liquid entry or exit port to the motor.

Rotating shaft angular velocity and torque.

Motor casing reference angular velocity and torque.

Input

expand all

Volumetric displacement of the motor, in m^3/rad, specified as a physical signal.

Motor efficiency for fluid displacement, specified as a physical signal. The value must be between 0 and 1.

Dependencies

To enable this port, set Leakage and friction parameterization to Input signal - volumetric and mechanical efficiencies.

Motor efficiency for the mechanical extraction of energy, specified as a physical signal. The value must be between 0 and 1.

Dependencies

To enable this port, set Leakage and friction parameterization to Input signal - volumetric and mechanical efficiencies.

Motor volumetric losses, in m^3/s, specified as a physical signal.

Dependencies

To enable this port, set Leakage and friction parameterization to Input signal - volumetric and mechanical losses.

Motor mechanical losses in N*m, specified as a physical signal.

Dependencies

To enable this port, set Leakage and friction parameterization to Input signal - volumetric and mechanical losses.

Parameters

expand all

Parameterization of the leakage and friction characteristics of the motor.

  • In the Analytical parameterization, the leakage flow rate and the friction torque are calculated by analytical equations.

  • In the Tabulated data - volumetric and mechanical efficiencies parameterization, the leakage flow rate and torque friction are calculated from the user-supplied Pressure drop vector, dp, Shaft angular velocity vector, w, and Displacement vector, D parameters and interpolated from the 3-D dependent Volumetric efficiency table, e_v(dp,w,D) and Mechanical efficiency table, e_m(dp,w,D) tables.

  • In the Tabulated data - volumetric and mechanical loss parameterization, the leakage flow rate and torque friction are calculated from the user-supplied Pressure drop vector, dp; Shaft angular velocity vector, w; and Displacement vector, D parameters and interpolated from the 3-D dependent Volumetric loss table, q_loss(dp,w,D) and Mechanical loss table, torque_loss(dp,w,D) tables.

  • In the Input signal - volumetric and mechanical efficiencies parameterization, the volumetric and mechanical efficiencies are received as physical signals at ports EV and EM, respectively.

  • In the Input signal - volumetric and mechanical loss parameterization, the leakage flow rate and friction torque are received as physical signals at ports LV and LM, respectively.

Amount of fluid displaced by shaft rotating under nominal operating conditions.

Dependencies

To enable this parameter, set Leakage and friction parameterization to Analytical.

Angular velocity of the shaft under nominal operating conditions.

Dependencies

To enable this parameter, set Leakage and friction parameterization to Analytical.

Motor pressure drop between the fluid entry and exit under nominal operating conditions.

Dependencies

To enable this parameter, set Leakage and friction parameterization to Analytical.

Ratio of actual flow rate to ideal flow rate at nominal conditions.

Dependencies

To enable this parameter, set Leakage and friction parameterization to Analytical.

Minimum value of torque to overcome seal friction and induce shaft motion.

Dependencies

To enable this parameter, set Leakage and friction parameterization to Analytical.

Ratio of actual mechanical power to ideal mechanical power at nominal conditions.

Dependencies

To enable this parameter, set Leakage and friction parameterization to Analytical.

Vector of pressure differential values for the tabular parameterization of leakage and torque friction. This vector forms an independent axis with the Shaft angular velocity vector, w and the Displacement vector, D parameters for the 3-D dependent Volumetric efficiency table, e_v(dp,w,D) and Mechanical efficiency table, e_m(dp,w,D) parameters. The vector elements must be listed in ascending order.

Dependencies

To enable this parameter, set Leakage and friction parameterization to either:

  • Tabulated data - volumetric and mechanical efficiencies

  • Tabulated data - volumetric and mechanical losses

Vector of angular velocity data for the tabular parameterization of leakage and torque friction. This vector forms an independent axis with the Shaft angular velocity vector, w and the Displacement vector, D parameters for the 3-D dependent Volumetric efficiency table, e_v(dp,w,D) and Mechanical efficiency table, e_m(dp,w,D) parameters. The vector elements must be listed in ascending order.

Dependencies

To enable this parameter, set Leakage and friction parameterization to either:

  • Tabulated data - volumetric and mechanical efficiencies

  • Tabulated data - volumetric and mechanical losses

Vector of volumetric displacement data for the tabular parameterization of leakage and torque friction. This vector forms an independent axis with the Shaft angular velocity vector, w and the Pressure drop vector, dp parameters for the 3-D dependent Volumetric efficiency table, e_v(dp,w,D) and Mechanical efficiency table, e_m(dp,w,D) parameters. The vector elements must be listed in ascending order.

Dependencies

To enable this parameter, set Leakage and friction parameterization to either:

  • Tabulated data - volumetric and mechanical efficiencies

  • Tabulated data - volumetric and mechanical losses

M-by-N-by-P matrix of volumetric efficiencies at the specified fluid pressure drop, shaft angular velocity, and volumetric displacement. Linear interpolation is employed between table elements. M, N, and P are the sizes of the corresponding vectors:

  • M is the number of vector elements in the Pressure drop vector, dp parameter.

  • N is the number of vector elements in the Shaft angular velocity vector, w parameter.

  • P is the number of vector elements in the Displacement vector, D parameter.

Dependencies

To enable this parameter, set Leakage and friction parameterization to Tabulated data - volumetric and mechanical efficiencies.

M-by-N-by-P matrix of mechanical efficiencies at the specified fluid pressure drop, shaft angular velocity, and displacement. Linear interpolation is employed between table elements. M, N, and P are the sizes of the corresponding vectors:

  • M is the number of vector elements in the Pressure drop vector, dp parameter.

  • N is the number of vector elements in the Shaft angular velocity vector, w parameter.

  • P is the number of vector elements in the Displacement vector, D parameter.

Dependencies

To enable this parameter, set Leakage and friction parameterization to Tabulated data - volumetric and mechanical efficiencies.

M-by-N-by-P matrix of volumetric leakage at the specified fluid pressure drop, shaft angular velocity, and displacement. Linear interpolation is employed between table elements. M, N, and P are the sizes of the corresponding vectors:

  • M is the number of vector elements in the Pressure drop vector, dp parameter.

  • N is the number of vector elements in the Shaft angular velocity vector, w parameter.

  • P is the number of vector elements in the Displacement vector, D parameter.

Dependencies

To enable this parameter, set Leakage and friction parameterization to Tabulated data - volumetric and mechanical losses.

M-by-N-by-P matrix of mechanical losses at the specified fluid pressure drop and shaft angular velocity. Linear interpolation is employed between table elements. M, N, and P are the sizes of the correlated vectors:

  • M is the number of vector elements in the Pressure drop vector, dp parameter.

  • N is the number of vector elements in the Shaft angular velocity vector, w parameter.

  • P is the number of vector elements in the Displacement vector, D parameter.

Dependencies

To enable this parameter, set Leakage and friction parameterization to Tabulated data - volumetric and mechanical losses.

Minimum value of volumetric efficiency. If the input signal is below this value, the volumetric efficiency is set to the minimum volumetric efficiency.

Dependencies

To enable this parameter, set Leakage and friction parameterization to Input signal - volumetric and mechanical efficiencies.

Maximum value of volumetric efficiency. If the input signal is above this value, the volumetric efficiency is set to the maximum volumetric efficiency.

Dependencies

To enable this parameter, set Leakage and friction parameterization to Input signal - volumetric and mechanical efficiencies.

Minimum value of mechanical efficiency. If the input signal is below this value, the mechanical efficiency is set to the minimum mechanical efficiency.

Dependencies

To enable this parameter, set Leakage and friction parameterization to Input signal - volumetric and mechanical efficiencies.

Maximum value of mechanical efficiency. If the input signal is above this value, the mechanical efficiency is set to the maximum mechanical efficiency.

Dependencies

To enable this parameter, set Leakage and friction parameterization to Input signal - volumetric and mechanical efficiencies.

Motor pressure drop that indicates the transition threshold between motor and pump functionality. A transition region is defined around 0 MPa between the positive and negative values of the pressure drop threshold. Within this transition region, the computed leakage flow rate and friction torque are adjusted according to the transition term α to ensure smooth transition from one mode to the other.

Dependencies

To enable this parameter, set Leakage and friction parameterization to either:

  • Tabulated data - volumetric and mechanical efficiencies

  • Input signal - volumetric and mechanical efficiencies

  • Input signal - volumetric and mechanical losses

Shaft angular velocity that indicates the transition threshold between motor and pump functionality. A transition region is defined around 0 rad/s between the positive and negative values of the angular velocity threshold. Within this transition region, the computed leakage flow rate and friction torque are adjusted according to the transition term α to ensure smooth transition from one mode to the other.

Dependencies

To enable this parameter, set Leakage and friction parameterization to:

  • Tabulated data - volumetric and mechanical efficiencies

  • Input signal - volumetric and mechanical efficiencies

  • Input signal - volumetric and mechanical losses

Volumetric displacement that indicates the transition threshold between motor and pump functionality. A transition region is defined around 0 cm^3/s between the positive and negative values of the displacement threshold. Within this transition region, the computed leakage flow rate and friction torque are adjusted according to the transition term α to ensure smooth transition from one mode to the other. It is also used to transition the ideal mass flow rate when the sign of D changes.

Whether to notify if the extents of the supplied data are surpassed. Select Warning to be notified when the block uses values beyond the supplied data range. Select Error to stop the simulation when the block uses values beyond the supplied data range.

Dependencies

To enable this parameter, set Leakage and friction parameterization to:

  • Tabulated data - volumetric and mechanical efficiencies

  • Tabulated data - volumetric and mechanical losses

Whether to notify if the block operates outside of the motor mode functionality. Select Warning to be notified when the block operates in the forward or reverse pump modes. Select Error to stop the simulation when the block operates in the forward or reverse pump modes.

Dependencies

To enable this parameter, set Leakage and friction parameterization to Input signal - volumetric and mechanical losses.

Whether to notify if the fluid at port A or B experiences low pressure. Select Warning to be notified when the pressure falls below a minimum specified value. Select Error to stop the simulation when the pressure falls below a minimum specified value.

The parameter helps identify potential conditions for cavitation, when the fluid pressure falls below the fluid vapor pressure.

Lower threshold of acceptable pressure at the motor inlet or outlet.

Dependencies

To enable this parameter, set Check if pressures are less than motor minimum pressure to either:

  • Warning

  • Error

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2020a