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e-Thermal is a vehicle level thermal analysis tool developed by General Motors to simulate the transient performance of the entire vehicle HVAC and Powertrain cooling system. It is currently in widespread (global) use across GM. This paper discusses the details of the air-conditioning module of e-Thermal. Most of the literature available on transient modeling of the air conditioning systems is based on finite difference approach that require large simulation times. This has been overcome by appropriately modeling the components using Sinda/Fluint. The basic components of automotive air conditioning system, evaporator, condenser, compressor and expansion valve, are parametrically modeled in Sinda/Fluint. For each component, physical characteristics and performance data is collected in form of component data standards. This performance data is used to curve fit parameters that then reproduce the component performance.

In recent years, climate protection has become as important as ozone layer protection was in the late 1980's and early 1990s. Concerns about global warming and climate change have culminated in the Kyoto Protocol, a treaty requiring its signatories to limit their total emission of greenhouse gases to pre-1990 levels by 2008. The inclusion of hydrofluorocarbons (HFCs) as one of the controlled substances in the Kyoto Protocol has increased global scrutiny of the global warming impact of HFC-134a (called R-134a when used as a refrigerant), the current mobile air conditioning refrigerant. Industry's first response was to begin improving current R-134a systems to reduce leakage, reduce charge, and increase system energy efficiency, which in turn reduces tailpipe CO2 emissions. An additional option would be to replace the current R-134a with a refrigerant of lower global warming impact. This paper documents the use of another HFC, R-152a, in a mobile A/C system.

The work presented in this paper outlines the design and development of a compliant sprocket for balancer drives in an effort to reduce the noise levels related to chain-sprocket meshing. An experimental observation of a severe chain noise around a resonant engine speed with the Dual-Mass Flywheel (DMF) and standard build solid (fixed) balancer drive sprocket. Torsional oscillation at the crankshaft nose at full load is induced by uneven running of crankshaft with a dual-mass flywheel system. This results in an increase of the undesirable impact noise caused by the meshing between the chain-links and the engagement/disengagement regions of sprockets, and the clatter noise from the interaction between the vibrating chain and the guides. This paper evaluates and discusses the benefits that the compliant sprocket design provided. A multi-body dynamics system (MBS) model of the balancer chain drive has been developed, validated, and used to investigate the chain noise.

The work presented in this paper outlines the development of a simulation model to aid in the design and development of a compliant sprocket for balancer drives. A design with dual-mass flywheel and a crank-mounted compliant chain sprocket greatly reduces interior noise levels due to chain meshing. However, experimental observations showed the compliant sprocket can enter into resonance and generate excessive vibration energy during startup. Special features are incorporated into the compliant sprocket design to absorb and dissipate this energy. Additional damper spring rate, high hysteresis and large motion angle that overlap the driving range may solve the problem during engine start-up period. This work develops a simulation model to help interpret the measured data and rank the effectiveness of the design alternatives. A Multibody dynamics system (MBS) model of the balancer chain drive has been developed, validated, and used to investigate the chain noise.

Flammability tests were conducted on one control HVAC module and two experimental automotive HVAC modules containing flame retardant chemicals. The HVAC modules were exposed to a heptane pool fire. All three HVAC modules burned under these conditions. The mass loss rates of the control and experimental HVAC modules were similar. The flame retardant chemicals caused a 50% reduction in the heat produced, a 751 - 897% increase in the carbon monoxide produced, a 4,867 - 5,567% increase in the gaseous hydrocarbon produced, and a 3,875 - 4,725% increase in the smoke produced when the HVAC modules burned under these conditions. These quantitative results are consistent with visual observations made during these tests that the experimental HVAC modules produced substantially more smoke than the control HVAC module.

Critical speed induced by imbalance forces is a well-known dynamic behavior of rotating shafts. Such problems are typically found in flexible shafts or rigid shafts with flexible supports when the frequency of rotation reaches the natural frequencies of the shaft. This simple critical speed problem is well understood and formulated in many engineering texts. However, not all critical speed phenomena are induced by imbalance. A perfectly balanced shaft with certain inertial properties also reaches a critical speed condition at a rotational speed that is not equal to the natural frequency of the shaft. Several variables of the dynamic system play a role on the critical speed condition, which is mainly induced by the unstable gyroscopic moment acting on the shaft. The unstable gyroscopic moment forces the shaft bearings to deflect causing precession about the undeflected geometric centerline of the shaft, but the rotation and precession speeds remain synchronized at low speeds.

Condenser, fan, radiator power train cooling module (CFRM) proposed by Delphi Automobile Systems was evaluated in the context of vehicle thermal system analysis. The results from the CFRM configuration were compared with those from the conventional condenser, radiator, and fan power train cooling module (CRFM). The analysis shows that for a typical passenger vehicle, the underhood temperature for the CFRM configuration is more than 10°C lower than its CRFM counterpart when the fan is operating at the same speed of 2500 rpm. This is due mainly to the higher mass flow rate impelled by the fan in the CFRM configuration. At the equal mass flow condition, both the CFRM and the CRFM configurations give similar underhood temperatures; but the fan in the CFRM configuration uses 19% less power, due mainly to the reduction in the fan speed needed to impel the same amount of mass flow rate.

The concept of condenser, fan, and radiator power train cooling module (CFRM) was further evaluated via three-dimensional computational fluid dynamics (CFD) studies in the present paper for vehicle at idle conditions. The analysis shows that the CFRM configuration was more prone to the problem of front-end air re-circulation as compared with the conventional condenser, radiator, and fan power train cooling module (CRFM). The enhanced front-end air re-circulation leads to a higher air temperature passing through the condenser. The higher air temperature, left unimproved, could render the vehicle air conditioning (AC) unit ineffective. The analysis also shows that the front-end air re-circulation can be reduced with an added sealing between the CFRM package and the front of the vehicle, making the CFRM package acceptable at the vehicle idle conditions.

Development and integration of the cooling system for an automotive vehicle requires a balancing act between several performance and styling objectives. The cooling system needs to provide sufficient air for heat rejection with minimal impact on the aerodynamic drag, styling requirements and other criteria. An optimization of various design parameters is needed to develop a design to meet these objectives in a short amount of time. Increase in the accuracy of the numerical predictions and reduction in the turn-around time has made it possible for Computational Fluid Dynamics (CFD) to be used early in the design phase of the vehicle development. This study shows application of the CFD for robust design of the engine cooling system.

CFD method for the calculation of flow rate and air re-circulation at vehicle idle conditions is described. A small velocity is added to the ambient airflow in order to improve the numerical stability. The flow rate passing through the heat exchangers is insensitive to the ambient velocity, since the flow rate is largely determined by the fan operation. The air re-circulation, however, is quite sensitive to the ambient air velocity. The ambient velocity of U=-1m/s was found to be the more critical case, and is recommended for the air re-circulation analysis. The CFD analysis can also lead to design modifications improving the air re-circulation.