6.4 Introducing Full-Vehicle Analyses

6.4.1 Full-Vehicle Analysis Process

You can take previously created suspension subsystems and integrate them with other subsystems to create a full-vehicle assembly. You can then perform various analyses on the vehicle to test the design of the different subsystems and see how they influence the total vehicle dynamics. You can also examine and understand the influence of component modifications, including changes in spring rates, damper rates, bushing rates, and antirollbar rates, on the total vehicle dynamics.

Figure 6.3 shows an overview of the process.

Figure 6.3 Full-Vehicle Analysis Process

6.4.2 About the Full-Vehicle Analyses

You can perform several types of full-vehicle analyses using ADAMS/Car. All of the analyses, except for the data-driven analyses, use the .__MDI_SDI_TESTRIG, and are therefore based on the Driving Machine.

The next sections describe the different types of analyses you can perform:

• Open-Loop Steering Analyses

• Cornering Analyses

• Straight-Line-Behavior Analyses

• Course Analyses

• Driver-Control-File-Driven Analysis

• Quasi-Static Analyses

• Data-Driven Analysis

• ADAMS/Driver Analyses

1. Open-Loop Steering Analyses

ADAMS/Car provides a wide range of open-loop steering analyses. In open-loop steering analyses, the steering input to your full vehicle is a function of time.

The open-loop steering analyses include:

Drift - In a drift analysis, the vehicle reaches a steady-state condition in the first ten seconds. A steady-state condition is one in which the vehicle has the desired steer angle, initial throttle, and initial velocity values. In seconds 1 through 4 of the analysis, ADAMS/Car ramps the steering angle/length from an initial value to a desired value. It then ramps the throttle from zero to the initial throttle value in seconds 5 through 10. Finally, it ramps the throttle value up to the desired value from a time of 10 seconds to the desired end time.

Fish-Hook - You use this analysis is to evaluate dynamic roll-over vehicle stability. The test is usually performed by driving at a constant speed, putting the vehicle in neutral, turning in one direction to a preselected steering wheel angle, and then turning in the opposite direction, to a final preselected steering wheel angle. You can define the duration of the step functions and the initial and final turn direction.

Impulse steer - In an impulse steer analysis, the steering demand is a force/torque, single-cycle, sine input. The steering input ramps up from an initial steer value to the maximum steer value. You can run with or without cruise control. The purpose of the test is to characterize the transient response behavior in the frequency domain. Typical metrics are: lateral acceleration, and vehicle roll and yaw rate, both in time and frequency domain.

Ramp steer - You use this analysis to obtain time-domain transient response metrics. The most important quantities to be measured are: steering wheel angle, yaw angle speed, vehicle speed and lateral acceleration. During a ramp steer analysis, ADAMS/Car ramps up the steering input from an initial value at a specified rate.

Single lane-change analysis - During a single lane-change analysis, the steering input goes through a complete sinusoidal cycle over the specified length of time. The steering input can be:

• Length, which is a motion applied to the rack of the steering subsystem.

• Angle, which is angular displacements applied to the steering wheel.

• Force applied to the rack.

• Torque applied to the steering wheel.

Step steer - The purpose of this analysis is to obtain time-domain transient response metrics. The most important quantities to be measured are: steering wheel angle, yaw angle speed, vehicle speed and lateral acceleration. During a step steer analysis, ADAMS/Car increases the steering input from an initial value to a final value over a specified time.

Swept-sine steer - Sinusoidal steering inputs at the steering wheel let you measure frequency-response vehicle characteristics. This provides a basis for evaluating a vehicle transitional response, the intensity and phase of which varies according to the steering frequency. The most important factors for this evaluation are: steering wheel angle, lateral acceleration, yaw speed, and roll angle. During a swept-sine steer analysis, ADAMS/Car steers the vehicle from an initial value to the specified maximum steer value, with a given frequency. It ramps up the frequency of the steering input from the initial value to the specified maximum frequency with the given frequency rate.