Car Automotive

Posts Tagged ‘vehicle’

Two trucks, one a pickup truck with a full-powered air bag for an unbelted occupant and the other an SUV (sport utility vehicle) with a depowered air bag for a belted occupant, were tested in 31 mph rigid barrier impacts. The essential data describing the vehicle and occupant responses are shown in Table 3.4. Truck #1 with an equivalent square wave (ESW) of 17.1g is stiffer than Truck #2 with an ESW of 14.7 g, and the peak torso deceleration of 51 g in Truck #1 is higher than that of 35 g in Truck #2.

The dynamic amplification factor (DAF) (ratio of the peak torso decelerations to vehicle ESW) is 3 for Truck #1 and 2.4 for Truck #2. Occupant performance in Truck #2 is superior to that in Truck #1 due to the lower torso g (deceleration).Referring back to the closed-form formula shown in Section 1.9.4 of Chapter 1, the peak occupant deceleration is a function of three factors: ESW, restraint stiffness, and restraint slack (or restraint contact time, t*).

It is shown that of these three factors, the controlling factors in the two cases are the ESW and restraint slack.the torso deceleration versus torso relative displacement for both trucks. The effective slack between the torso and the shoulder belt in the left front occupant of Truck #2 is almost zero, while that for the Truck #1, *1, is about five inches, this being the distance between the fully deployed air bag and the left front occupant torso.
The higher torso deceleration in Truck #1 is attributed to the unbelted condition. The occupant simply freely flew into the deployed air bag. The left front occupant horizontal motion in Truck #1 forces the steering column to stroke and rotate upward, resulting in head-windshield contact.

Among the various modes of vehicle crashes, rollover crashes are often very severe and threatening events that involve automotive vehicles. Rollover occurs as a result of complex interactions among the driver, the vehicle, and the environment.

It may be precipitated from one or a combination of factors. Rollover may be initiated on a flat and level road surface such as when making a steady turn. Once the lateral acceleration acting on a vehicle exceeds rollover threshold for that vehicle, the wheels on one side of the vehicle lift up from the road surface, and the vehicle begins a rollover process. Rollover may also occur after a vehicle slides sideway and hits a curb.

In this situation, the vehicle acquires a large angular velocity due to the sudden stopping of the sliding vehicle upon hitting the curb. In this section, the fundamentals of vehicle rollover dynamics, including rollover detection methodology, are introduced. Other factors such as handling, suspension, and tire properties, the vehicle geometry including wheelbase, the driver, and the complex road conditions are beyond the scope of this text.

In the development of a new vehicle platform, its crashworthiness is an important concern, and it is imperative to compare the impact severity of the vehicle and occupants under various test and design conditions. Since an impact is a physical event that involves analyses of impulses and energy components, such as kinetic energy, energy absorption, and energy dissipation, the analyses require both the principle of work and energy and that of impulse and momentum.

Although both principles are derived from Newton’s Second Law, they are not mutually exclusive when it comes to solving problems involving impact and excitation.It will be shown that any crash event, modeled by either a single-mass or a multi-mass system,involves impact and/or excitation. Case studies, such as the dynamic principles of pyrotechnic pretensioner on the occupant responses, are investigated. The preloading effect of a restraint system on the occupant response and ridedown efficiency are discussed.

Many crashworthiness topics related to single and multi-vehicle collisions are analyzed by the engineering principles presented so far for determining the degree of crash severity. Applications of these principles to vehicle-to-vehicle compatibility, shear loading of truck body mounts due to eccentric loading, and the methodology of accident reconstruction methodology are also presented.

In the development of a new vehicle platform, its crashworthiness is an important concern, and it is imperative to compare the impact severity of the vehicle and occupants under various test and design conditions. Since an impact is a physical event that involves analyses of impulses and energy components, such as kinetic energy, energy absorption, and energy dissipation, the analyses require both the principle of work and energy and that of impulse and momentum. Although both principles are derived from Newton’s Second Law, they are not mutually exclusive when it comes to solving problems involving impact and excitation.

It will be shown that any crash event, modeled by either a single-mass or a multi-mass system,involves impact and/or excitation. Recognizing the existence of the impact and/or excitation, the closed-form formulas  utilized to solve problems. Case studies, such as the dynamic principles of pyrotechnic pretensioner on the occupant responses, are investigated.

The preloading effect of a restraint system on the occupant response and ridedown efficiency are discussed. Many crashworthiness topics related to single and multi-vehicle collisions are analyzed by the engineering principles presented so far for determining the degree of crash severity. Applications of these principles to vehicle-to-vehicle compatibility, shear loading of truck  body mounts due to eccentric loading, and the methodology of accident reconstruction methodology are also presented.