CASE STUDY

Customer

AM General

OpenECU for Developing Semi-Active Suspension Control

Challenge

To develop a control system for semi-active suspension for AM General’s BRV-O program that met all the performance and reliability requirements for a US military tactical wheeled vehicle program.

One of the challenges developing an adjustable suspension control system was to calculate the intended vehicle path, and resolve the precise amount of ride height change for each strut-corner.  This was critical, as over-control is certainly possible given the performance of the hydraulic components, which could lead to instability of the chassis during dynamic driving events.

Solution

Working with the suspension system component suppliers and the vehicle manufacturer, Pi Innovo’s systems engineering team used the OpenECU M461 rapid control prototyping controller and custom-developed model based control software, validated on  Hardware-In-Loop (HIL) test rigs, to control the system.  Control features include an electrically-drive hydraulic pump and electromechanical valves to control hydraulic fluid pressure in each wheel corner strut, a steering wheel angle sensor and dashboard buttons for mode selection, and wheel position and suspension strut pressure sensors to provide feedback on vehicle behaviors.

Pi Innovo addressed the challenges of preventing over-control by developing an algorithm for ride height adjustment based on measured ride height at each strut corner, as well as measured strut pressure for each corner.  Using sensor fusion techniques, Pi Innovo was able to combine these signals with vehicle inertial measurements as well as driver steering inputs to derive the appropriate amount of control for each strut-corner.  This vehicle-based approach allowed the system to be precisely tuned to optimize vehicle mobility across a varied set of terrains/speeds.

There are several modes of operation where these type of controls are useful: leveling the vehicle when parked on a slope (for loading and occupant ingress/egress), lowering for transportation, raising the vehicle for water fording, and dynamically adjusting during cornering or braking events to reduce body roll and pitch.

The controller hosts a comprehensive diagnostics package.  The controller not only identifies component failures, but monitors the overall performance of the suspension system and adjusts the controls to provide the optimal remedial action for any given failure.

Results/Impact

Utilizing the capabilities of the OpenECU development environment Pi Innovo’s systems engineering team was able to develop a control system for several different iterations of semi-active suspension on various prototype vehicle platforms in reaction to evolving requirements, ultimately providing a validated solution for the JLTV program intended for production in 2016.

Pi Innovo was able to reduce development time and costs by leveraging Hardware-In-Loop (HIL) simulation to test a majority of the controls before integration on a vehicle.  Through HIL testing, Pi Innovo simulated many of the scenarios and use cases that the system experiences on the vehicle.

Along with simulation testing, the semi-active suspension system has been tested across more than 500,000 miles of varied terrain and operational environments.  The suspension system has provided vehicles not only the mobility to traverse severe off-road conditions, but also provided a safe, stable platform to operate at high speeds on prepared surfaces.

Project Features

Systems engineering
Rapid controls prototyping
Custom embedded control software development
HIL testing
Validation testing

Duration

2009 to 2015