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Automotive manufacturers have intensified their efforts to increase vehicle fuel economy by reducing weight without sacrificing vehicle size and comfort. Vehicle areas that offer the potential to reduce weight include chassis structural components. A cradle or a subframe is a chassis structural component that is utilized to support the engine/powertrain in front wheel drive vehicles. Traditionally, engine cradles have been manufactured by using stamped steel weldments. Recently, automotive designers are considering alternative processes, i.e., hydro-forming, as well as fabricating engine cradles using lightweight materials. The objective of this paper is to describe the development of an aluminum engine cradle for a General Motors's midsize vehicle. The design criteria and structural performance requirements for this cradle are presented along with an overview of the manufacturing processes used to produce this lightweight structural part.

The effects of strain-rate and element mesh size on the numerical simulation of an automotive component impacted by a mass dropped from an instrumented drop tower was investigated. For this study, an analysis of a simple steel rail hat-section impacted by a mass moving at an initial velocity of 28Mph was performed using the explicit finite element code Radioss. Three constitutive material models: Elasto-Plastic (without strain rate), Johnson-Cook, and Zerilli-Armstrong were used to characterize the material properties for mild and high strength steel. Results obtained from the numerical analyses were compared to the experimental data for the maximum crush, final deformation shape, average crush force and the force-deflection curve. The results from this study indicate that the mechanical response of steel can be captured utilizing a constitutive material model which accounts for strain rate effect coupled with an average mesh size of 6 to 9mm.

The new regulations to reduce emissions have resulted in the development of new techniques to maintain or enhance competitive performance. A requirement for the manifold is to help meet the reduction in cold start emissions, particularly during the transient conditions from start to 100 seconds following the Federal Test Procedures for vehicle emissions. Finite element computer models were developed to predict inner and outer wall temperatures, and to determine structural soundness. Tests were performed to assure that noise levels were minimized. Dynamometer lab and field tests were performed to verify that the manifold would meet the design requirements. From the results of these tests and analyses, modifications were made to the weld and manufacturing techniques to improve product life and reduce noise. Dual wall manifolds have proven durability to meet high exhaust gas temperatures up to 1650°F (900°C), while meeting the performance, noise, and weight reduction goals.

Over the past 20 years, polyvinyl chloride (PVC) has almost replaced metal in stationary glass reveal moldings with dramatic part cost savings on cars and trucks world-wide. The process of assembly is generally simple and convenient but to replace a reveal molding can be difficult. Many times, in order to replace the molding, it may also be necessary to replace or reseal the glass. In short, PVC reveal moldings, relatively inexpensive parts, are very expensive to service. Outside of general assembly and processing issues, there are 5 variables that may cause a failure in the performance of a stationary glass reveal molding. They are as follows: material degradation, crystallization, plasticizer loss, material properties, and molded-in stress. Because of modern standard PVC formulations and the material requirements of most automotive companies, material degradation, crystallization and plasticizer loss do not commonly cause failure. Material properties and molded-in stress do.

In an effort to reduce anisotropy, which affects sheet forming performance, special actions were taken in the production of 6009-T4 sheet. To further reduce anisotropy in forming behavior, the modified 6009-T4 sheet was given an electro-discharge texture (EDT) surface topography to make friction behavior nondirectional. The modified 6009-T4 was compared to standard 6009-T4 in terms of metallurgical characteristics, laboratory test results and field forming results. The modified sheet yielded reduced planar anisotropy and improved formability. EDT completely removed directionality in friction behavior and led to an improvement in performance in the forming trials.

Aluminum sheet forming is entering an era where rapid advances in technology are likely. Combining increased understanding of material behavior, increased understanding of metalworking tribology and improved control of sheet forming processes will result in improved distribution of strain, allowing more complex components to be formed and greater design flexibility. New process control techniques will be developed and implemented to result in improved press actions, control of strain path to effect increased formability and reduced sensitivity to process variables. Improved techniques for assessing producibility and for generating effective tool designs will be developed, perhaps eliminating the need for soft tool tryouts to substantially reduce the total die development time and cost. In this review paper, each of these issues will be discussed.

The analytical methods for single leaf steel springs should at least include two areas: (1) allowance for any curved or tapered shape, and (2) technologies to precisely predict the geometrical configuration due to large deflection. The last item is an outstanding consideration in automotive application because of the parts alignment requirement. In this paper, a practical analytical method is presented to achieve the goals mentioned above. Basically, the. flexibility method of finite element was employed in the solution technique. In the spring application, this approach can save computer time because of the elimination of matrix inversion in the internal computation. An integration form of the flexibility matrix for each element was given in this paper to allow for a tapered spring shape. This integration-formed flexibility matrix can be approximately evaluated by the Gaussian Quadrature Formula.

An automated engine dynamometer test procedure is developed and mathematical models for the main engine control variables are derived from the resulting data base. The new procedure involves sequential testing at many speed/load conditions for various combinations of air fuel ratio, spark timing and exhaust gas recirculation. The total testing time required for generating the data base of more than 2000 test points is less than twelve hours. An independent transient speed/load test is also conducted for the purpose of validating the engine models. The measured and model predicted data are compared for this test which corresponds to a segment of the EPA urban schedule.

Three-way catalysts provide a means of catalytically achieving lower NOx emission levels while maintaining good control of HC and CO emissions. However, very accurate control of air-fuel ratio is necessary. The precise air-fuel ratio control required is accomplished by employing a closed loop fuel metering system in conjunction with an exhaust gas sensor and an electronic control unit. To gain production experience with this type of system, General Motors is introducing it on two 1978 engine families sold in California. One is a 2.5 litre L-4 engine and the other is a 3.8 litre V-6 engine. Closed loop controlled carburetors are used on both systems. This paper discusses these 1978 systems. The components used on both systems are described and emission and fuel economy results are reviewed.

The Experimental Safety Vehicle powertrain and fuel system developed by General Motors in compliance with Contract DOT-OS-00095 with the U.S. Department of Transportation include several special features: a low engine accessory package to meet the front visibility down angle of 8 degrees, engine and transmission mounting for retention at high decelerations, a light aluminum engine, an over-the-rear-axle fuel tank, and a unique evaporative emission fuel pipe routing. A comprehensive test program was planned and final testing to validate contract specifications was conducted.

A comprehensive cycle analysis has been developed for four-stroke spark-ignited engines from which the indicated performance of a single cylinder engine was computed with a reasonable degree of accuracy. The step-wise cycle calculations were made using a digital computer. This analysis took into account mixture composition, dissociation, combustion chamber shape (including spark plug location), flame propagation, heat transfer, piston motion, engine speed, spark advance, manifold pressure and temperature, and exhaust pressure. A correlation between the calculated and experimental performance is reported for one engine at a particular operating point. The calculated pressure-time diagram was in good agreement with the experimental one in many respects. The calculated peak pressure was 10 per cent lower and the thermal efficiency 0.8 per cent higher than the measured values. Thus this calculational procedure represents a significant improvement over constant volume cycle approximations.