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The necessity for avoiding the occupant ejection from their seats during motor coach rollover accidents is of supreme importance. The seat belt as a safety device is the best practical way of achieving this task. As per the motorcoach Enhanced Safety Act of 2009 passed in the United States senate, requires new motorcoaches to be installed with safety belts for each seating position. This bill also suggests the possibility of retrofitting seat belts on the existing motorcoaches. The use of portable seatbelt to restraint occupant is more economical as compared to retrofit the seat belt. This fact motivates the further research on portable restraint device. This paper demonstrates the evaluation of the first version of the Portable Restraint Device (PRD) using full scale bus rollover test. This test identified the shortcoming of this current device in securing to the bus seat and its non user friendly design.

Rear axle tramp can be excited by rough roads or cyclic vertical inputs from tire failure. If the excitation frequency is at or above the natural frequency of the axle/tire spring-mass system, the response can be sufficient to cause loss of control due to axle tramp, which will cause decreased lateral friction of the rear tires resulting in oversteer. Recognition of this problem led to this study of the mechanics of the rear axle motion during controlled cyclic inputs. Tramp response to cyclic impacts or imbalance is analyzed theoretically and compared to measured responses on a vehicle. The effects of axle moment of inertia, spring stiffness and placement, and shock stiffness and placement are discussed. Testing of a vehicle with a controlled vertical impact to the rear axle was conducted in an SAE J266 circle maneuver to determine the effects of tramp magnitudes and frequency to the understeer characteristic of the vehicle and reported in a previous paper [1].

Typically the roll propensity of a vehicle is calculated from the assumption that the vehicle is a rigid body and that its roll propensity can be determined by taking the ratio of the track width and the center of gravity height. However, a passenger vehicle is not a rigid body; it is at least two rigid bodies connected through links and springs and shock absorbers. The objective of this paper is to derive a new second order rollover metric, which will predict whether a vehicle may be susceptible to rollover from simple physical measurements of the vehicle. The validation of the derived metric using a stock and modified vehicle configuration will be presented. Further validation with several vehicles is planned and will be reported in later papers.

Occupants of off-road vehicles are very susceptible to the effects of vertical accelerations. Root mean square values normally accepted are 0.25 g's for longer duration and 0.4 g's for a shorter duration (up to two hours per day) (ref. 1). Typical off-road vehicles stiffen the suspension in order to prevent bottoming of the vehicle. This causes the ride to be extremely rough, meaning the vertical accelerations are at the limit of the human endurance. The speed of the vehicle is then limited by the endurance of the individual. By lengthening the suspension travel and tuning the spring stiffness and damping coefficients, a smooth and controllable ride is achieved thus increasing the natural limit speed. “Whoop-de-doos” are referred to by off-road drivers as a set of evenly spaced waves in the path of travel. These are often caused by repeated traffic over a soft surface. These bumps are sinusoidal in nature and are usually spaced 6 meters apart and 0.2 meters high.

Can a buckle designed with a lock for the latch when struck on the face, back, or side, also have this same feature when accelerated along the longitudinal axis? Six seatbelt buckles from various manufacturers were tested to determine their dynamic characteristics in the longitudinal direction along the mounting stalk. Patented designs of the buckles were intended to prevent inertial unlatching of the buckle. Although they may perform well in lateral and vertical directions, when force is applied along the direction parallel to the mounting stalk the buckles could be made to release. If the buckle is mounted in the vehicle with a rigid stalk, could impact pulses be transmitted to the buckle to cause release? A test apparatus was constructed where the buckle could be mounted with the stalk and webbing. The webbing could be preloaded and the buckle was accelerated by impacting the mounting point at the base of the stalk.

This paper discusses the modeling of vehicle rollover collisions and resulting occupant motions. MADYMO is used to model a completely instrumented NHTSA dolly rollover collision of a Bronco II. Animated modeled motions are compared to actual video footage of the rollover. Measured acceleration pulses from the test are compared with the computed accelerations of the vehicle center of gravity, and driver head and chest accelerations. Also the vehicle roll velocity test data are compared to the computed values. It was found that there was good agreement between the modeled and test results. From the results, we discuss the capability to determine the injury of the occupant from the computed results.

In modeling the mechanics of an ATV in acceleration, stopping, hill climbing or descending maneuvers, it is necessary to understand the nature of the frictional forces on the tires of the vehicle. The tire's force characteristics in the longitudinal direction are not as simple as for automotive tires acting on paved surfaces. The interaction of the lugs of the tires with the soil, grass, rocks, roots, and surface anomalies all affect the longitudinal forces transmitted to the vehicle. The typical modeling of the tire's interaction as a force being equal to the normal force times some constant friction coefficient is totally inadequate. Unlike normal tires, the ATV tire has a pulsing effect while at limit conditions. Even on level pavement the pulsing persists which indicates that is not necessarily a surface interaction phenomenon. The frictional spikes are significantly above 1.0 rising as high as 1.89 and will affect one's prediction of the motion of the vehicle.

There have been documented cases of rollover accidents wherein the driver was ejected while wearing the single loop lap/shoulder harness. Three actual incidents will be discussed here. In two of the three cases the vehicle was photographed at the accident scene with the latchplate still in the buckle, whereas in the other case, the evidence of the seatbelt having been latched was found some time after the accident. Rollover accidents are second to frontal collisions in severe injury causation. It is an accepted fact that retention in the vehicle is necessary for an occupant to have a chance at mitigating the injuries associated with a rollover event. It is also the purpose of the seatbelts to restrain the occupant and prevent ejection in this kind of vehicle accident. In this paper, the design of the seatbelt retractor will be analyzed to determine its role in the retention of occupants in a rollover collision.

A four degree of freedom model of a single passenger off-road vehicle (ATV) is presented. A designer may use the model to study the effects of spring stiffnesses, damping coefficients in bump and jounce, tire stiffnesses, center of gravity placement, and vehicle moment of inertia on the vertical bouncing and pitching motion of the sprung and unsprung masses over any terrain profile. In order to isolate the effects of the rider, he is modeled as if in the posting position as a mass concentrated at the foot pegs.

With the advent of the Emergency Locking Retractors (ELRs) in the seventies, the mechanism of the seat belt safety system started becoming increasingly complex. The ELRs were made either webbing sensitive or vehicle sensitive. The former type contained an inertial device that activated after sensing webbing acceleration. The latter contained an inertia responsive pendulum mass and had the ability to lock-up whenever the vehicle experienced a sudden change in velocity or a sudden tilt or rotation. In this paper, the ELR mechanisms that employ the pendulum-pawl system are discussed and their susceptibility to fail under certain conditions investigated. The present research was conducted to evaluate the effectiveness of the ELR mechanisms and identify those conditions where the ELR was least effective.

Using the validated computer model described in reference (1), general design rules of thumb are developed for the design of single passenger off-road vehicles (ATV). The question of spring stiffness balance from front to rear is discussed along with the effects of damping ratios in jounce and rebound, and tire/suspension stiffness ratio, and suspension travel. The design objective is to minimize vehicle bounce and pitch accelerations transmitted to the rider and to maintain as flat of a riding position as possible.

This paper describes the performance and behavior of a Stirling cyrocooler incorporating a working fluid composed of helium and nitrogen. At the operating temperature of the cryocooler (80 K), the nitrogen component will condense in the freezer section. It is shown that the phase change in the working fluid increased the heat lifted for a given size and weight of machine and the coefficient of performance. The magnitude of these effects was dependent on the mass ratio of nitrogen to helium, phase angle between the compression and expansion processes, and the ratio of the compression space volume to the expansion space volume. The optimum heat lifted performance was obtained for a mass ratio of four parts of nitrogen to one part of helium, a phase angle of approximately 100 degrees, and a volume ratio of two which resulted in a heat lifted increase of 75% over the single phase, 90 degree phase angle configuration. The coefficient of performance showed a 20% improvement.

A technique has been devised whereby brake thermal characteristics may be determined by measuring brake temperature, vehicle velocity, and braking torque over a wide range of operating conditions. The relationships between these experimental parameters are then determined using statistical methods of regression analysis. With the use of computer data acquisition systems, and the relative ease with which massive amounts of data may be accumulated, mathematical relationships may be developed. These rather simple mathematical relations then can be used to indicate such complex phenomena such as heat transfer coefficients from the brake surface.

A brake has been designed for use on a class 8 tractor trailer which utilizes a hydrodynamic film of fluid between a series of rotors and stators to reduce wear and increase energy rejection capability. The hydrodynamic film brake or HFB was constructed and tested on a brake dynamometer and demonstrated a very low parasitic loss at all speeds and a high energy rejection rate. Deceleration rates of a 10,450 kg (23,000lb) inertially simulated axle were 6 M/S2 (20 ft/s2) with the application of 0.618 MPa (90 PSI) air pressure. These tests demonstrated the feasibility of meeting the braking requirements for class 8 vehicles with a wet disc brake. Test results indicated very low wear rates for in service operation and good heat rejection characteristics.

GMI Engineering & Management Institute uses the SAE Supermileage Competition as a means of enhancing the design aspect of its engineering curriculum. The project is integrated into senior level courses and involves many students each year. GMI’s 1982 effort emphasized maximizing engine efficiency via a re-designed combustion chamber, 12:1 compression ratio, and an overhead valve train. Chassis work centered upon minimum weight and drag losses. Official performance was 350 mpg. Engine starting difficulties and unforeseen chain drive reliability problems detracted from performance. Ambitious plans for 1983 include a complete new vehicle designed by 1982 veterans, and a re-designed version of GMI’s 1982 car implemented by a new crew.