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A comprehensive test program was conducted to correlate aerodynamic drag measurements from the General Motors Aerodynamics Laboratory with coastdown results. An improved method of coastdown testing was used to minimize the sources of error in determining aerodynamic drag. Several vehicles were tested, covering a large range of aerodynamic drag values, representative of current and future production vehicles. Wind tunnel and coastdown results were determined to be in good agreement, with an average drag coefficient difference of only. 008 (2%).

AS a basis for the analyses of this symposium, a hypothetical car has been used to evaluate the engine power distribution in performance. Effects of fuel,-engine accessories, and certain car accessories are evaluated. The role of the transmission in making engine power useful at normal car speeds is also discussed. Variables encountered in wind and rolling resistance determinations are reevaluated by improved test techniques. Net horsepower of the car in terms of acceleration, passing ability and grade capability are also summarized.

A requirement for larger trucks and higher operating speed is indicated. The present report presents wind tunnel data on drag of a Chevrolet truck-trailer combination. Possible means of drag reduction are examined. Although side force and yawing moment data are presented, their effect on directional stability are not, at present analyzed.

A detailed description of the oxidative stability of GM's DEXRON®-VI Factory Fill Automatic Transmission Fluid (ATF) is provided, which can be integrated into a working algorithm to estimate the end of useful oxidative life of the fluid. As described previously, an algorithm to determine the end of useful life of an automatic transmission fluid exists and is composed of two simultaneous counters, one monitoring bulk oxidation and the other monitoring friction degradation [1]. When either the bulk oxidation model or the friction model reach the specified limit, a signal can be triggered to alert the driver that an ATF change is required. The data presented in this report can be used to develop the bulk oxidation model. The bulk oxidation model is built from a large series of bench oxidation tests. These data can also be used independent of a vehicle to show the relative oxidation resistance of this fluid, at various temperatures, compared to other common lubricants.

General Motors Powertrain Division has developed a new V-8 engine for Cadillac vehicles in the 1990s. The Northstar engine incorporates the use of aluminum for both the cylinder block and head and other lightweight materials throughout. The valve train incorporates direct acting hydraulic lifters actuating the four valves per cylinder through dual overhead camshafts. The primary focus of the project has been to produce an engine of unquestioned reliability and exceptional value which is pleasing to the customer throughout the range of loads and speeds. The engine was designed with a light weight valve train, low valve overlap and moderate lift, resulting in a very pleasing combination of smooth idle and a broad range of power. The use of analytical methods early in the design stage enabled systems to be engineered to optimize reliability, pleaseability and value by reducing frictional losses, noise, and potential leak paths, while increasing efficiency and ease of manufacture.

This paper describes the methodology used to achieve optimum aerodynamic performance of the 1992 through 1995 Oldsmobile Cutlass Supreme IMSA GT race car and will demonstrate the continuous improvements successfully used to respond to rule changes and competition. The concerted effort by the sanctioning body to limit the aerodynamic performance of IMSA GT race cars for the 1995 season required a rigorous wind tunnel test program backed by track validation to maintain the necessary aerodynamic balance, cooling flows, engine induction flow, and overall competitive parity. The specific modifications that were evaluated to accommodate these rules changes will be detailed in this paper. Special test methodologies developed to better understand specific aerodynamics questions such as the effects of vehicle attitude, internal cooling flows, underbody treatments, and engine air inlet performance will also be discussed.

This paper describes the design, synthesis-analysis and development of the unique vehicle structure architecture for the fifth generation Chevrolet Corvette, ‘C5’, which starts in the 1997 model year. The innovative structural layout of the ‘C5’ enables torsional rigidity in an open roof vehicle which exceeds that of all current production open roof vehicles by a wide margin. The first structural mode of the ‘C5’ in open roof configuration approaches typical values measured in similar size fixed roof vehicles. Extensive use of CAE and a systems methodology of benchmarking and requirements rolldown were employed to develop the ‘C5’ vehicle architecture. Simple computer models coupled with numerical optimization were used early in the design process to evaluate every design concept and alternative iteration for mass and structural efficiency.

This paper describes some methods for greatly reducing or possibly eliminating subjective tuning of suspension parts for ride and handling. Laptop computers can now be used in the vehicle to guide the tuning process. The same tools can be used to select solutions that reduce sensitivity to production and environmental variations. OBJECTIVE Reduce or eliminate time required for tuning of suspension parts for ride characteristics. Improve the robustness of ride performance relative to variations in ambient temperature and production tolerances. PROBLEM REQUIRING SOLUTION AND METHOD OF APPROACH Traditional development programs for new vehicles include time-consuming subjective ride evaluations. One example is shock absorber tuning. Even if sophisticated models define force-velocity curves, numerous hardware iterations are needed to find valvings that will reproduce the curves. Many evaluation rides are needed to modify the valvings to meet performance targets.

Typically, “Reliability and Maintainability (R&M)” is perceived as a tool for products alone. Putting emphasis on reliability only at the cost of maintainability is another archetype. Inclusion of both reliability and maintainability (R&M) in all the phases of the machinery and equipment (M&E) life cycle is required in order to be world competitive in manufacturing. R&M is mainly a design function and it should be a part of any design review. Inclusion of the R&M concept early in the life cycle of M&E is key to cost effective and competitive manufacturing. Neither responsive manufacturing nor preventive maintenance can raise it above the level of inherent R&M.

HOW well are multigrade oils performing at low temperatures? An investigation has shown that the low-tem perature properties of mulrigrade oils are often not equivalent to the single-grade oils-lOW in a mulrigrade oil may actually be 20W. One phase of this investigation, a full-scale cranking study using commercial 10W and 10W-30 oils in cars at 0 F, is discussed in detail in this paper.

The work presented here builds on the practical and effective spot weld fatigue life prediction method, the structural stress method (SSM), that was developed at Stanford University. Constant amplitude loading tests for various spot weld joint configurations have been conducted and the SSM has been shown to accurately predict fatigue life. In this paper refinements to the structural stress approach are first presented, including a variable amplitude fatigue life prediction method based on the SSM and Palmgren-Miner's rule. A test matrix was designed to study the fatigue behavior of spot welds under tensile shear loading conditions. Constant amplitude tests under different R-ratios were performed first to obtain the necessary material properties. Variable amplitude tests were then performed for specimens containing single and multiple welds.

Robust optimization usually requires numerous functional evaluations, which is not feasible when the functional evaluation is time-consuming. Examples in automobile industry include crash worthiness/safety and fatigue life simulations. In practice, a response surface model (RSM) is often used as a surrogate to the CAE model, so that robust optimization can be carried out. However, if the error in the RSM is significant, the solution based on the RSM can be invalid. This paper proposes a method of finding multiple candidate solutions, all of which have similar predicted performances. This approach is effective in finding the close-to-optimum solutions when the model has error, and providing design alternatives. Examples are provided to illustrate the method.

Since 1997, General Motors Body Manufacturing Engineering - Die Engineering Services (BME-DES) has been working jointly with our software vendor to develop and implement a parallel version of stamping simulation software for mass production analysis applications. The evolution of this technology and the insight gained through the implementation of DMP/MPP technology as well as performance benchmarks are discussed in this publication.

During early 2005 General Motors released a newly developed ATF for the factory fill of all GM Powertrain stepped gear automatic transmissions. The new fluid provided significantly improved performance in terms of friction durability, viscosity stability, aeration and foam control and oxidation resistance. In addition, the fluid has the potential to enable improved fuel economy and extended drain intervals. Since the performance of the new fluid far exceeded that of the DEXRON®-III service fill fluids available at the time it became necessary to upgrade the DEXRON® service fill specification in order to ensure that similar fluids were available in the market for service and repair situations. This latest upgrade to the service fill specification is designated DEXRON®-VI [1].

A front suspension laboratory test procedure was developed to reproduce time-correlated fatigue damaging events from a light truck road durability test. Subsequently, the performance of front suspension systems for the GMT 400 light truck program were evaluated in terms of customer reliability. Both prototype and pilot testing, as well as computer modeling, were used in the evaluation.

Free form fabrication, or rapid prototyping as it is commonly known, is the creation of a physical entity, directly from numerical description, using an additive process. The mathematical data used is typically in the form of a 3D CAD file, but it may also be obtained from a reverse engineering process. This paper presents a review of three of the leading FFF (free form fabrication) systems which are commercially available. Time constraints will allow us to describe only three of these products. Although this does not do justice to a technology where there are more than 30 different systems in various stages of development, these examples represent the vast majority of machines which are in the marketplace today.

The potential of bake hardenable steel as a substitute for SAE 1008 steel to reduce gage and improve dent resistance is investigated in this report. Outer body panels in particular are susceptible to palm printing and other forms of denting. Conventional SAE 1008 steel and a developmental continuous annealed bake hardenable steel from Inland Steel Company are compared for dent performance properties. Bake hardenable (BH) steel is a medium strength (200-350 MPa) steel that receives an increase in yield strength during the heating of the paint bake cycle. An increase in yield strength would result in an increase in dent resistance. The increase in dent resistance is more quantitatively evaluated by comparing the BH steel with the current production material (SAE 1008) of a rear compartment lid outer.

The performance of potential sulfate sorbents was evaluated using an engine-dynamometer screening test procedure. Bulk and supported sorbents were tested. The two most promising sorbents were a bulk CaO preparation and alumina supported Na. The CaO sorbent appeared to be inherently non-selective between sulfates and SO2. Calcining this sorbent in a CO2 atmosphere resulted in increased pellet crush strength and reduced volume expansion upon use. The Na/Al2O3 sorbent had good activity and selectivity, but may lack capacity and be subject to leaching losses of Na-compounds. Vehicle and dynamometer durability testing of these two sorbents was conducted. From these preliminary tests, it was determined that neither met all the criteria of an ideal sorbent for vehicle use.

Brake caliper and corner behavior in the off-brake condition can lead, at times, to brake system performance issues such as residual drag (and related issues such as pulsation, judder, and loss of fuel economy), and caliper pryback during aggressive driving maneuvers. The dynamics in the brake corner can be strikingly complex, with numerous friction interfaces, rubber component and grease dynamics, deflections of multiple components, and significant dependence on usage conditions. Displacements of moving parts are usually small, and the residual forces in the caliper interfaces involved are also small in comparison with other forces acting on the same components, making direct observation very difficult. The present work attempts to illuminate off-brake behavior in two different conditions - residual drag and pryback - through the use of low-range pressure distribution sensors placed in between the caliper (pistons and fingers) and the brake pad pressure plates.

This paper summarizes the design, development, fabrication, validation, and application of a new device called the Skin Thermal Transducer (STT). The development of this instrument was driven by the demand for reliable information on human skin temperatures during contact with a warm surface on the interior of an automobile. The primary technology that enabled the development of the STT was the thermo-electric cooler (TEC) in combination with a heat sink that is used to simulate the core temperature of the human body. The STT was validated with human skin data and the agreement was within an acceptable range. The STT provides the automotive engineer with a measuring device to optimize and validate the underbody regions of the vehicle with respect to occupant thermal comfort. The STT can also be applied to optimize other automotive and non-automotive products in which the human skin touches a warm surface.