Torque Converter

Viscous fluid coupling between rotating driveline shafts

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Simscape / Driveline / Couplings & Drives

Description

A torque converter couples two driveline axes, transferring torque and angular motion by the hydrodynamic action of a viscous fluid. Unlike a friction clutch, a torque converter cannot lock the axes together. The Torque Converter block acts between the two ports I and T. The block acts as a lookup function of the relative angular velocity of the two connected driveline axes. This function is defined at discrete angular velocities. For model details, see Torque Converter Model.

Ports and Conventions

The impeller or pump port I and turbine port T are rotational conserving ports.

The Torque Converter block follows these conventions:

• The impeller port I is the port that connects to the engine, and the turbine port T is the port that connects to the load. In normal operation, power thus flows from the impeller to the turbine.

• Forward power flow implies power flowing from I to T. Reverse power flow implies power flowing from T to I.

• The power input is through the shaft with the larger speed. The power output is through the shaft with the smaller speed.

Parameters

Torque Characteristics

Speed ratio vector

Vector of values of the independent variable, the dimensionless speed ratio R_ω. You must order these values in ascending order.

Torque ratio vector

Vector of values of the block function's first dependent variable, the dimensionless torque ratio R_τ. Each torque ratio value corresponds to a speed ratio value.

Capacity factor parameterization

Definition of the capacity factor, either K (ratio of impeller speed ω_I to square root of impeller torque τ_I) or K^* (ratio of τ_I to ω²_I). The default is K.

Capacity factor reference speed

Choice of speed in the capacity factor definition, depending on speed ratio R_ω. Select either:

• Impeller speed ω_I for all values of R_ω.

• Impeller speed ω_I for R_ω < 1, and turbine speed ω_T for R_ω > 1.

Capacity factor vector

Vector of values of the block function's second dependent variable, the torque conversion capacity factor K. Each capacity factor value corresponds to a speed ratio value.

From the drop-down list, choose units.

• If you choose the default capacity factor definition K, the default units are radians/second/√(newton-meters) (rad/s/(N*m)^0.5).

• If you choose the alternative capacity factor definition K^*, the default units are newton-meters/(radians/second)² (N*m/(rad/s)^2).

Interpolation method

Interpolates torque ratio and capacity factor functions between discrete relative velocity values within the range of definition. The default is Linear.

Extrapolation method

Extrapolates torque ratio and capacity factor functions outside the range of definition. The default is Linear.

Dynamics

Model transmission lag

Select how to model transmission lag from input to output driveshaft. The default is Specify time constant and initial torque.

• No lag — Suitable for HIL simulation — Torque transfer is instantaneous.

• Specify time constant and initial value — Torque is transferred with a time lag. If you select this option, the panel changes from its default.

   Time Constant and Initial Torque Ratio

  Torque transmission time constant

  Dynamic torque transfer time constant t_c. The default is 0.02.

  From the drop-down list, choose units. The default is seconds (s).

  Initial turbine-to-impeller torque ratio

  Ratio of turbine torque τ_T to impeller torque τ_I at the start of the simulation.

Torque Converter Model

The torque converter is a mechanism for transferring torque between impeller and turbine shafts. Because the coupling of I and T occurs by viscous action, the torque transfer depends on the difference ω = ω_T – ω_I ≠ 0, or the speed ratio R_ω ≠ 1. In normal operation, the two axes have different speeds, and the output axis speed never exactly reaches the input axis speed. The torque transfer is largest when R_ω → 0 or ∞, and shrinks as R_ω → 1. Because R_ω can never reach exactly one, a torque converter always transfers some torque.

Speed Ratio, Torque Ratio, and Capacity Factor

You specify the torque ratio and the capacity factor of the torque converter as discrete functions of the speed ratio with tabular vector entries. The three vectors of the variable values must have the same length.

• The speed ratio R_ω is the turbine angular speed divided by the impeller angular speed:

  R_ω = ω_T/ω_I .

• The torque ratio R_τ is the output (turbine) torque divided by the input (impeller) torque:

  R_τ = τ_T/τ_I .

• The capacity factor K or K^* is defined in two ways for R_ω < 1, with either the default or the alternative definition:

  • Default, the input speed divided by the square root of the input torque:

    K = ω_I / √τ_I .

  • Alternative, the input torque divided by the square of the input speed:

    K^* = τ_I / ω²_I .

• The capacity factor reference speed for R_ω > 1 is ω_I by default. That is, the input speed ω_I is used in the ratio that defines either K or K^*.

  For R_ω > 1, the alternative choice for reference speed is to replace ω_I by the output speed ω_T in this defining ratio.

The two dependent variables, R_τ and K, are functions of the independent variable R_ω. They specify the characteristics of the torque converter:

R_τ = R_τ(R_ω) , K = K(R_ω) .

Continuation Near Speed Ratio of Unity

If you do not specify capacity factor data for a speed ratio of 1, the block uses a capacity factor value of 10*K_Max, where K_Max is the maximum value in the specified capacity factor vector. The corresponding torque ratio is assumed to be 0. For all other speed ratio values not explicitly specified in the lookup table data, the block uses the interpolation or extrapolation method selected in the block dialog box.

Instantaneous Torque Transfer

When there is no time lag, the input impeller (I) and output turbine (T) torques are:

τ_I = sgn(1 – ω_T/ω_I)·[ω_I / K]² , τ_T = τ_I·R_τ ,

in normal operation (forward power flow).

Lagged Torque Transfer

You can optionally include the effect of torque transmission time lag, caused by internal fluid flow and compressibility. Instead of τ_T and τ_I being instantaneously constrained to one another, a first-order time lag introduces a delayed response in the impeller torque:

t_c·(dτ_I/dt) + τ_I = τ_I(steady state) .

The preceding instantaneous function of the capacity factor K determines the steady-state value of τ_I.

Limitations

The impeller shaft must always rotate in a positive direction. Simulation is not valid for ω_I < 0.

If you drive the Torque Converter from a torque source, such as the Generic Engine, you must include an inertia in the source, to represent the engine, shaft inertia, or other source components. To ensure that the impeller starts by rotating in a positive direction, set the initial speed for this inertia to a positive value.

Torque Transmission Time Lag

Torque converters lag in their response to changing input torque. By default, Torque Converter includes no time lag in its response. You can include a response lag by specifying a time constant. Time lag simulation increases model fidelity but reduces simulation performance. See Adjust Model Fidelity.

Real-Time Simulation

Hardware-in-the-Loop Simulation

For optimal simulation performance, for the Dynamics > Model transmission lag parameter, select No lag - Suitable for HIL simulation.

Reference

Society of Automotive Engineers, Hydrodynamic Drive Test Code (Surface Vehicle Recommended Practice), SAE J643, May 2000.

Extended Capabilities

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