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Model rolling resistance
The block models the resistance force that acts on the wheel hub due to the rolling resistance at the road-wheel contact surface. The model can use a constant resistance coefficient or the pressure and velocity dependence of the SAE J2452 standard. The resistance force is zero when the normal force acting at the wheel-road surface is less than or equal to zero.
In the constant coefficient model, the rolling resistance is directly proportional to the resistance coefficient:
F=Nμ
where parameters represent the following quantities:
F — Rolling resistance force
N — Normal Force
μ — Rolling resistance coefficient
The rolling resistance coefficient has a hyperbolic form that eliminates discontinuity at v_{hub}=0:
μ=μ_{0}tanh(4v_{hub}/v_{threshold})
where parameters represent the following quantities:
μ_{0} — Asymptotic rolling resistance coefficient
v_{hub} — Hub velocity
v_{threshold} — Threshold velocity
The pressure- and velocity-dependent model uses the following formula:
$$F={\left(\frac{P}{{P}_{0}}\right)}^{\alpha}{\left(\frac{N}{{N}_{0}}\right)}^{\beta}{N}_{0}\cdot \left(A+B\left|{v}_{hub}\right|+C{v}_{hub}{}^{2}\right)$$
where parameters represent the following quantities:
P — Tire pressure
v_{hub} — Hub velocity
α, β, A, B, C — Approximating coefficients
P_{0} — 1 Pascal (Pa)
N_{0} — 1 Newton (N)
In the previous equation, parameters P_{0} and N_{0} remove the physical units from each exponential expression base.
Connection H is a mechanical translational conserving port that represents the hub of the tire. Connection N is a physical signal input port that represents the normal force acting on the tire. Normal force is positive if it points downward.
Select the model used to compute the rolling resistance on a wheel hub. The parameter provides two options:
Constant coefficient
Pressure and velocity dependent
The default value is Constant coefficient.
Selecting the Constant coefficient option exposes two model parameters: Constant coefficient and Velocity threshold.
Coefficient that sets the proportionality between the normal force and the rolling resistance force. The parameter must be greater than zero. The default value is 255.
Velocity at which the full rolling resistance force is transmitted to the rolling hub. The parameter ensures the force remains continuous during velocity direction changes, which increases the numerical stability of the simulation. The parameter must be greater than zero. The default value is 0.001 m/s.
Inflation pressure of the tire. The parameter must be greater than zero. The default value is 250e+3 Pa.
Exponent of the tire pressure in the model equation. See Pressure and Velocity Dependent Model. The default value is -0.003.
Exponent of the normal force model equation. The default value is 0.97.
Velocity independent force component in the model equation. The parameter must be greater than zero. The default value is 84e-4.
Velocity dependent force component in the model equation. The parameter must be greater than zero. The default value is 6.2e-4 s/m.
Force component that depends on the square of the velocity term in the model equation. The parameter must be greater than zero. The default value is 1.6e-4 s^2/m^2.
Velocity at which the full rolling resistance force is transmitted to the rolling hub. The parameter ensures the force remains continuous during velocity direction changes, which increases the numerical stability of the simulation. The parameter must be greater than zero. The default value is 1e-3 m/s.