Ride Height Sensors
Ride height sensors are used in conjunction with Truck air springs. Truck air springs include an auto-trim feature, where you can specify a desired trim height of the suspension and the air spring's trim load is automatically adjusted during static equilibrium analysis to achieve the trim height.
A ride height sensor consists of an arm attached by a revolute joint to the vehicle's frame, and a link attached to the arm and the suspension by constant velocity and spherical joints, respectively. The sensor is located in the model by specifying three coordinate references. The angle between the arm and the link is the measured quantity. The measurement can be tuned to represent actual ride height control valves using two parameters:
■ride_height_sensor_deadband - angular value representing allowed suspension travel (as measured at the ride height sensor) before the trim load will be adjusted.
■ride_height_sensor_time_constant - time value representing the time constant of a first-order lag applied to the measurement.
Creating and Modifying Ride Height Sensors
To create a ride height sensor in the Template Builder:
1. From the Build menu, point to Parts, point to Truck Ride Height Sensor, and then select New.
3. Select OK.
To modify a ride height sensor in the Template Builder:
1. To display the Modify dialog box, do one of the following:
♦From the Build menu, point to Parts, point to Truck Ride Height Sensor, and then select Modify. To load the parameters for a specific ride height sensor, you must specify the ride height sensor you want to modify.
♦Right click on a ride height sensor, point to its name, and then select Modify. The dialog box has the ride height sensor parameters already loaded.
3. Select OK.
When working in Standard Interface, you can only modify ride height sensors. Learn about the
Interface Modes.
To modify a ride height sensor in the Standard Interface:
1. Right click on a ride height sensor, point to its name, and then select Modify. The dialog box has the ride height sensor parameters already loaded.
3. Select OK.
Using with Truck Air Springs
The ride height sensor contains an Adams Solver differential equation. This differential equation may be used to set any number of Truck air spring trim loads. The differential equation calculates the trim load that corresponds to the desired ride height during static equilibrium analysis. In Automatic-Fixed mode, its value is then locked to the last value calculated during static analyses for all the subsequent transient simulations:
F = IF(MODE - 5: 0, -1000 * ride_height_measure_realtime, 0)
In Automatic-Variable mode, its value is calculated once during static analysis, but then allowed to vary for all the subsequent transient simulations:
F = IF(MODE - 5: -1000 * (sign(1, ride_height_measure_delayed)
* step(abs(ride_height_measure_delayed), 0.9 * deadband/2, 0, deadband/2, 1)), -1000 * ride_height_measure_realtime, 0)
where:
■ride_height_measure_realtime - is the angle between ride height sensor arm and link. When the change in this angle exceeds half the deadband, the trim load will be increased or decreased accordingly.
■ride_height_measure_delayed - is the filtered ride height measurement. The ride height sensor parameter named ride_height_sensor_time_constant affects the filter.
■deadband - is an angular value representing the allowed suspension travel (as measured at the ride height sensor) before the trim load will be adjusted.