The Relation of Riding-Quality to Angular Car-Acceleration 290002
THIS paper describes the use of the gyro-accelerometer, an instrument capable of recording angular velocity, angular acceleration and the total angle turned. The design and development of this instrument came as a result of research into the riding-quality of automobiles, which work demonstrated the necessity of measuring angular motions in a moving car under road conditions, a task that was impossible to accomplish with the equipment that was then available.
To avoid taking a great number of readings and obtain a basis of comparison, a standard test, consisting of driving a car over a special bump at different speeds and plotting curves of the resulting angular quantities as given by the gyro-accelerometer, was devised. This test is known as the standard-bump test, and the values of maximum angular acceleration obtained at different speeds are evidently closely related to riding-quality. To establish this relation, tests were made by this method at Iowa City, Iowa, and at the proving grounds of the General Motors Corp. and the Studebaker Corp. While making these tests, the opinions of the company drivers were recorded. Curves were plotted of these opinions and of the values of angular acceleration. The similarity of the curves indicates the close relationship between riding-quality and angular acceleration. This relationship allows riding-quality to be evaluated numerically so that cars of different makes tested at different times and localities can be tabulated as to riding-quality without making direct comparison. It also eliminates the factor of variable personal feeling at the time of comparisons.
A standard of riding-quality to be known as the University of Iowa Standard Riding Scale is proposed, based on the maximum angular-acceleration values recorded by the gyro-accelerometer when using the standard-bump test. This makes possible the rating of cars in terms of standard riding-quality.
Attention is called to other uses for the gyro-accelerometer in connection with automobile design, such as that of selecting the proper spring and shock-absorber equipment so that the combined action will give the best riding-quality, and that of determining instantaneous centers about which a car oscillates, for use in locating the best weight-distribution and determining the proper location of spring supports. The instrument can also be used to determine the angle of roll and the angle at which skidding occurs, in obtaining the effect of the height of the center of gravity.
A method is outlined whereby the instrument can easily be adapted, by the addition of integrating mechanism, to furnish the total amount of all angular velocities or accelerations or the total number of times certain values of angular velocities or accelerations have been encountered in a road test.