Search Results

This paper summarizes an experimental study of an isolated bluff body in ground effect and the same body with the addition of nearby non-rotating wheels. First, theoretical and experimental trends relating to ground proximity and diffuser mechanics are reviewed. Next, experimental forces and flow patterns for a body alone were found, resulting in a maximum lift coefficient of approximately 0.80. Subsequently, the addition of stationary wheels, not attached to the body, significantly diminished the downforce generation by as much as 65%. Quantitative trends as well as tuft and neutrally buoyant bubble flow observations were carried out to infer the appropriate flow physics. Specifically, it is concluded that the wheels decrease body downforce by impeding the creation of strong vortices in the diffuser, deflecting flow in a potential manner, and introducing energy dissipating wake turbulence into the diffuser.

This paper describes an automatic stabilizing technique to prevent tractor jackknifing in tractor-semitrailer trucks. This stabilizing technique consists of the detection of the onset of a jackknife and the subsequent application of corrective action. The onset of a jackknife is detected through the behavior of the drive wheels, and the corrective action consists of a form of corrective braking; that is, the simultaneous operation of the antiskid systems at all axles of the truck. The results obtained in this study indicate that the stabilizing technique may effectively prevent the development of a tractor jackknife during braking. Furthermore, the implementation of this technique in a real truck would be relatively simple and require a minimum of additional hardware.

This paper describes the addition of tandem-drive axles and tractor suspension dynamics to a digital computer model of a tractor-semitrailer truck. The extended model provides 22 degrees of freedom for the vehicle. Two degrees of freedom are included for the motion of each tractor axle; vertical tire flexibility, tandem-axle suspension jacking, and tandem-axle roll steer are also included in the extended model. The features of the previous vehicle model (based on the work of Mikulcik) are retained in the extended model. These features include nonlinear equations for translation, yaw, pitch, and roll of both the tractor and the semitrailer (except as these motions are constrained by the fifth wheel), wheel rotation dynamics, and antiskid brake control. The model also includes a simulated “driver” which specifies the steering angle and the air pressure applied to the brakes.

A computer model of a tractor-semitrailer is developed which extends that given by Mikulcik in SAE 710045 (Ref. 10 of paper). The extended model allows translation, yaw, roll, and pitch of both tractor and semitrailer. Lateral and fore-and-aft weight transfer is displayed. Wheel dynamics are included, and effects of wheel slip, slip angle, vehicle speed, and tire load are used in the calculation of the tire forces. The vehicle is maneuvered by a simulated driver who specifies the front-wheel steer angle and the brake torques. The ability of the model to accurately describe a real vehicle is studied by using the model to simulate a full-scale experimental test. The model is also used to study two types of proportional braking for a tractor-semitrailer executing a large-radius turn on a wet asphalt track.