Even today, automakers still rely on the subjective evaluations of test engineers when assessing the handling properties of motor vehicles. However, objective evaluation methods using measurable characteristics are growing more important. Objective assessments can reveal even small steps in development progress better than any subjective evaluation could.
Myriad sensors measure both what the driver is doing and how the vehicle is moving. To capture the driver’s actions, sensors measure steering wheel angle and moment, brake pedal travel and force, and accelerator pedal travel. To capture what the car is doing, sensors measure the triaxial forces and moments at the contact area between the road and the tires, as well as wheel speed; wheel position in X, Y and Z; and the toe and camber angles of each wheel. Additionally, the motion parameters of the vehicle’s body (triaxial angles, speeds and accelerations related to the vehicle’s center of gravity) and the deviation from a reference course are determined. Since the sensors cannot be located directly at the center of gravity, coordinate transformations are required.
To assess steering angle, torque and speed, Kistler has developed the Measurement Steering Wheel (MSW). The MSW mounts between the steering wheel and the steering shaft. A central aperture makes mounting easy. To permit universal application, an adapter for connection to the steering shaft gearing can be produced to any specification.
The MSW comes in two models—a 50 newton-meter version for passenger cars and a 250 newton-meter version for trucks.
Steering torque is measured with an integrated strain gauge. Steering angle and speed are measured with a noncontact optical encoder with a resolution of up to 7,200 pulses per rotation.